Setting up a fish tank, whether you're keeping puffs or any other fish, is a process which requires some foresight and planning.  Going out and buying a prepackaged system is usually not a good idea, as some of the components associated with such marketing ploys are of poor quality.  Knowing what you (actually, your fish) need and accommodating this will save you a lot of hassle and stress in the long run.

Size
The first step of choosing your new ecosystem is size.  SIZE MATTERS!!  The larger your tank, the more stable it will be.  Larger bodies of water are more resistant to major changes in parameters such as ph, temp, etc.  Bigger tanks are also easier to clean, as you'll have much more room to maneuver the siphon or hose around as you suck up the detritus at the bottom of your tank.  Try to choose a tank that is the largest you can manage, understanding you'll have to be able to do things such as water changes.  Since you already know that the bigger the tank the more expensive it will be, take into consideration that this is a logistical thing.  The price of components for your tank will also rise as you choose larger vessels.  The bottom line is pufferfish need room.  If you want a suggestion go somewhere between 29 gallons (110 liters) and 50 gallons (189 liters).  Don't get a 20 gallon (78 liter) tank if you plan on keeping more than one puffer.  Puffers tend to orient (although not exclusively) on the bottom of the tank, so longer tanks with more bottom surface area are better than the "high" variety.  As a general rule, give each puffer about 20 gallons of space, taking into account the size of your current tetroadont.  Additionally, the more room you give them the less likely they are to end up fighting each other, as many species can be quite territorial.  Some will fight for food regardless, but sometimes this can't be helped.  Giving puffers ample space also lets them have more to explore, which is fun to watch.  I'm convinced this adds to their overall health as well.

Tank composition, namely acrylic or glass, is of concern as well.  Acrylic tanks are fine, with the exception of durability.  Acrylic tanks tend to scratch more easily, which can be frustrating considering you may need to clean the front of the tank from time to time. They are also harder to clean.  I highly recommend glass.  This really affects you more than your puffer.

Lighting
Lighting your tank is important too.  Most tanks will some with a hood sold as a package, and that's
probably your best bet.  This will save you the hassle of trying to match up a hood and tank should
you purchase them separately.  Check the inside of the hood to see what length the bulbs will be, and understand you will probably have to get another bulb.  This goes back to the marketing geniuses who can make a little more money by packaging an inferior bulb in the hood.  You need to decide at this point whether you'll be keeping live plants with your puffers, since they require special light to thrive.  You'll see a difference in your tank as well, as lights that mimic sunlight are healthier.  One of the factors involved in choosing your bulb is light penetration.  The taller your tank is, the less light will penetrate to the floor of your tank.  This is of significance depending on what type of flora you'll be planting.  Another factor is wattage. The wattage of your bulb will affect your tank from both a heat and radiant intensity perspective.  High wattage radiates ambient heat, and raises the temperature of your tank.  The intensity of light affects plant growth.  For more on plants, you can check the "Plants for your puffer"  section of this website using the navigation bar at the bottom of the page. (or click the link)  I've done fine with Power-glow bulbs, which have a high red and blue output.

Filtration
Of all the components in your setup, filtration is the most important.  Puffers tend to prefer live or frozen foods.  While interesting and let's face it--cool, this is a messy way to eat.  Waste tends to build up in the form of uneaten food, whether it be leftover (stop stuffing your fish!!) or particles of food that fall into the substrate at the bottom of your tank.  This detritus accumulates and slowly breaks down into various compounds which are toxic to your puff.  As you can see, good filtration is a must.  The filtration in a fish tank has three main constituents: biological, mechanical, and chemical.

Biological filtration is the key filter in your system.  The removal of ammonia from your puffer's water is of prime importance.  This is done by establishing the nitrogen cycle in your tank with the two beneficial bacteria (nitrobacter, nitrosomonas).  Not establishing this filter will inevitably kill any fish, regardless of what kind of filter you buy. Ok, enough said.  If you want to explore this topic in depth, click the bacteria.  There are 3 main places for these beneficial bacteria to live in your tank.
Biowheels are one place.  I am a big proponent of biowheel media, which are external filters that hang off of your tank and remove large particulate while running the water over a wheel which contains the bacterial colony before returning the water to your tank.  This allows the bacteria to remove the ammonia and nitrite from your water quite effectively.  It also maintains the colony in a protected area, so when you vacuum or do water changes you are not removing substantial numbers of the bacteria.  Penguin is one manufacturer of this type of media, and also makes Emperor.  Emperor is simply a larger version of the Penguin Biowheel, for bigger tanks.  It comes with a premixed cartridge of carbon, which unfortunately can't be accessed.  Some aquarists don't appreciate this, and tend to stay

Mechanical Filtration is quite easy.  There are tons of external power filters on the market.  Since nitrobacter and nitrosomonas live on the porus surface of your gravel, having a biowheel isn't mandatory.  Most filters on the market allow you to fill the media with your own carbon or whatnot, and usu. cost less than the Penguin.  Whisper is a large manufacturer of this type of filter.  The amount of noise generated by filters is really of personal taste, and I say this because some filters are noisier than others.  The main function concerning mechanical filtration is the removal of large particles in the water before they can sink into the gravel and break down into ammonia.  Most filters on the market handle this well.

Chemical Filtration usually takes place inside the cartridges of the filters above.  Carbon removes many of the toxins from your tank (including tetrodotoxin).  If you have a filter that allows you to mix your own chemical media, you may think about using mixtures containing ammo-zorb, zeolite,
phospho-zorb, or any other toxin removing substance you need.  This type of filtration is more of a temporary solution to toxicity problems.  They are helpful if you experience a major spike in say-- ammonia, but if your biological filter is set up correctly you shouldn't have these problems often.  You may also utilize this type of filtration if you want to recondition your water because of some undesirable conditions (e.g. changing the hardness of your water).

Since most puffers are tropical fish, you'll need a heater.  I recommend a submersible heater of adequate size for your tank.  Check the packaging or ask your local fish dude (or girl) at the LFS.  Keep in mind that these heaters, while somewhat accurate with their settings, aren't always precise.  Because of this, you should also have a separate thermometer.  These come in as many sizes and setups as there are people.  Whatever works for your aquarium will be fine.  Just make sure you position the thermometer far enough from your heater so you can take accurate readings that will reflect your entire tank.  Since we are talking temperature, you should note where you are going to place your tank.  Sunlight and other factors concerning temperature should also be considered.

Lastly, but not unimportantly, you'll no doubt be purchasing tank decorations.  By this I mean gravel, rocks, wood, etc.  There is a practical end to this.  While I'm not going to suggest aesthetics, you should give your puffer some places where it can feel safe.  Their natural habitat offers them places to avoid predation and rest as well.  Providing such places is of great benefit, as your puffer will undoubtedly appreciate them.  Puffers are also used to foraging for various prey.  Rock formations and large pieces of driftwood (or fake wood) accommodate them well.  Check with your LFS if you are using real wood, as this can alter your water chemistry.  Plants work well too.  I highly suggest getting
live plants, which add both beauty and stability to your tank.  If not, there are tons of plastic look-alikes which can shelter your puff as well.
Gravel is another component which adds to your tank.  Most gravel you'll find at your LFS is coated with epoxy.  This is normally done so that minerals and/or dyes present in the rock doesn't seep into your water.  Puffers will generally prefer rounder stones to sharp ones, as they tend to rest on the bottom from time to time.  Crushed coral is available too, but realize this is not coated with epoxy and will alter the chemistry of your water (raises the hardness).  You can also use just about anything found in nature, although I wouldn't suggest it.  Rocks and other items can contain harmful compounds.  I don't suggest using anything that is not meant for your tank.  Personal taste aside, you may want to consider some other factors when picking tank decorations.  You can read about this in the "Holistic Approach to Keeping Puffers" page.  Anyway, this is the fun part...I'll leave you to it.