looks great but you need to remove those shims before you fill up the tank. those kind of point pressure sources will crack the bottom glass.
as you have found in your research, glass tanks only need corner support and no metal (steel or iron) stands are perfectly straight. so gaps in the middle are fine, the bottom glass is designed to support the full weight of the tank. as long as the corners are well supported you should be good. contrary to popular internet misinformation, gaps between tank and stand in the middle are fine (even a big long gap, its normal with metal tube stands). even the manufacturers will tell you this.
styrofoam will not help (all it does is compress more at the corners and not as much at the middle where the bow of the stand is, so the middle is just as unsupported as it is without the styrofoam). Aqueon tanks are designed to sit directly on the stand with nothing in between (I have an aqueon 150g on a tube steel stand, my stand is the same) long gap lol). I believe styro actually voids the aqueon warranty, as the tanks are not meant to have anything between the tank rim and stand.
seeing those shims like that was scaring me, don't wan't to see 180g of water on the floor.
otherwise, awesome build! please keep up the good work!