As others have said you are headed for even more troubles than you realize with a stocked tank that probally hasn't even started to cycle, you chances of keeping the nems are slim to none in a new tank that still has to cycle. 3-6 weeks for a cycle, then only a cuc, and then a few weeks later a single small fish and a few weeks later another ect. After 3 months you might be ready for some easy corals 9-12 months, maybe a nem and many before you also thought that their tank was different but they never are.
But as far as your brace problem, as others have suggested, try and get a new top, buy I would drain the tank part way and take the stress off of it, if you want to fixe it, get some weld on and acrylic and make 2 new pieces to sandwich the broken piece in-between. You will have to get the gap in the old brace closed before doing it. Weld on will fuse the pieces all together. Care will been takes not to get any of it in the tank.
Also it broke while setting up a phosphate reactor, you don't need one, save your money, wc
is all you need to keep most reefs successful.