1st, I'm a glass kind of a guy... never owned a plastic tank. But. I've got a bunch of friends that do, or have.
Properly bonded acrylic is STRONG. Stronger than silicone sealed glass. One of the things that make it strong is that it is flexible. A 1/2" bow over a large acrylic panel would not scare me. That euro bracing you've got, once again, provided it's properly bonded, adds TONS of rigidity to the tank. Nothing you've shown or said would bother me in the least. Friend of mine has a 250g acrylic system, it's thinner than yours, and bows a good bit more. No problem.
Splitting, cracking, crazing, seams coming loose... get it empty now. But a bit of a bow? No problem. Same 1/2" bow on a glass tank? I'd be worried as hell!
Now... that advice and the guarantee that comes along with it is worth just exactly what you paid for it. Nothing.
Here's an absolutely solid fact for you: Your tank will fail. They all do... eventually. Our tanks are either glass sealed with silicone, which breaks down over time, or cast acrylic bonded with resin, which also breaks down over time. How much time? Depends... on far too many variables for anyone around here to give an accurate estimate.
Setting a large container full of salt water in your living room is a risk. Don't believe me? Ask your insurance agent what they'll pay for damage caused by that tank failing. The usual answer is the same as I'm going to send you if your tank breaks immediately after I told you not to worry about it. If you choose to pursue this hobby, long term, you are almost certain to have a tank failure causing some amount of water damage eventually. All you can do is try and minimize the risk. Pay attention to the tank, seal condition, stand condition, plumbing, overflow, sump, ATO system... anything that could make a real mess should be inspected regularly.
