It is usually better to spend more $$$ and get more equipment. That said, if you are on a budget, you CAN keep a very nice FO tank. Your options are just a bit more limited.
Your tank is approx. 48L x 30H x 18W, correct? At those measurements and at 120g, I would keep fish that will only get to about 8" max.
Since you are new to saltwater, I would stick to fish that are generally regarded as "hardy" and can take less-than-perfect water conditions. There are a hundred choices of hardy fish under 8". Pick 10 or so out that you like and ask us which ones will get along together, and how many of them should be kept in that size tank. Get on some vendor sites now, and then crosscheck their adult sizes with
www.fishbase.org Fishbase has the most accurate measurements on fish - much more trustworthy than most vendor sites.
A Fluval 404 and Biowheels can work, but the Fluval especially can be labor intensive. Plus these are not as effective as sump/refugium systems. BUTTTT -- you are on a budget, so for now keep what you have, understanding that you have to do weekly water changes, change your filter media religiously, and monitor and test all the time. You have less room for error.
Given your system, skip corals, shrimp, crabs, etc. which are not as hardy as most fish. As a bonus, you can keep regular NO lights on your tank, you won't need PC or metal halide.
Once you get rolling and are having success, you can upgrade 6-12 months down the road if you wish. But for now, YES you can have a nice FO tank on a budget -- as long as you accept the limitations of a non-fancy system.
Best of kuck to you!
welcome again!
