Note that you have a lot of option when it comes to DIY project, and it may help to think outside of the box a little bit.
Acrylic and glass may be the first thing come to mind, but in my experience they are difficult to work with if you're a new to it. Especially if you gonna do the scoring/cut and finishing yourself (which IMO equally important if not more than the assembly step itself). That's even more so if you're working with acrylic. Without proper scoring and proper surface finishing step, your weld almost guarantee to fail even before you do it. It's best to have whatever place you buy from to cut and finish/polish it for you, and even then if the company don't normally do it for aquarium building, you'll have to double check their work. It would be best to start out with a small project - like a 5-10g and see if you can make it water-tight with your technique before attempting a bigger project.
On the other hand, plywood + epoxy may not be what people think about, but they actually much easier to work with. The main reason is because the error margin is much larger, and you can over-engineer to the point it will compensate any mistake you may make. With glass, there is only so much silicon you can use until it looks ridiculous, with acrylic either you make the perfect weld or a bad weld, you can not "overweld" to be sure (since it's chemical welding).
Here is a few picture of my first project, a 200g tank made from 3/4" plywood.
- The panels are hold together with 2" long nail/screw + super-wooden glue. They're then braced with 1" lumber around the base and top. If you are unsure, feel free to throw on a couple extra metal corner bracer.
- The inside are coated with epoxy. Again if you're not sure about your current coats, you can always put on another one, and another one, and another until you feel confident.
- The seams are line with fiberglass cloths, with epoxy painted on top, followed by silicone.
That tank basically was built to widthstand even an earthquake ... I think, and I never had any experience with woodworking prior, basically was just youtubing the whole process. And I think it looks fairly decent. I built it to house the baby koi you saw swimming in there. Years later when they got big, I built another 1000g tank to house them, also from wood (but line with pond liner instead of epoxy) to the cost of about 1$ per gallon. So you can't beat the price.