Tetraodon nigroviridis - Green Spotted Puffer
Not exactly a small puffer to keep, grows to 6.8 inches / 17cm and minimum tank 30 gals US / 110 litres according to Seriously Fish website.
So thats the first thing you need, a minimum of 30 gals, though a bigger tank is always better.
You do not mention what your water parameters are in terms of general hardness / softeness, as well as pH. This is important information as you may have water that may be unsuitable for GSP. You can find this information from your local water supplier website, should be pages of various information and stats, what you want to look for is the part with water hardness information and post the numbers on here, we will then advise further.
As for other species to keep with this GSP, that SF link says -
"
Can be kept in a community tank, but caution should be exercised when choosing tankmates, as it tends to nip the fins of slow-moving or long-finned fish. Some individuals also become particularly spiteful with age. It’s best kept with robust, active species such as scats, archerfish, Arius catfish and perhaps monos."
These puffer scan be kept in freshwater, but they tend to live longer and only spawn in brackish. For a tank of 30 gals you would be advised that it's best only to keep one GSP but in a much larger tank you may get a group but they are aggressive towards own species, not the best idea if you are not that experienced a fishkeeper and may not know what to look out for.
Having said all that I think it makes more sense to stay with freshwater, as brackish requires salinity knowledge and would be a steep learning curve. I have not done any brackish tanks but would consider for the new fishkeeper this is as a bit of a leap as is not as straightfowards as freshwater or full marine set ups.
As for fishless cycling the tank, this article will help a great deal -
Cycling Your New Fresh Water Tank: Read This First!
For cycling puposes, you will need -
1 - A water test kit to test for Ammonia, Nitrite and Nitrate (as well for pH). API Freshwater Master Kit is a popular choice and is adequate for this process. i would advise not to get these strip paper dip kits, not reliable and can be found to be inaccurate.
2 - You will need a bottle of ammonia, these can be fairly easily obtained online, either as ammonia purely for fishless cycling or you can get a bottle of Kleen Off is a popular choice and can be found in certain hardware stores in USA. Think ACE ammonia is another choice found in ACE hardware store if theres one nearby to you. What you want is basically just ammonia and water, ammonium hydroxide and no other chemical ingredients at all.
3 - Follow that article i linked, and the last requirement is - patience, lots of it!
Set up the tank as you want it, substrate, plants, decor, heater, filter, lights and all the rest of it, once satisfied, start your fishless cycle as its easier to leave the tank alone while the tank and filter goes through the process of cycling.