The whole shebang's gonna weigh around 65 odd kgs yeah?That's not really significant, I wouldn't bother with central support, just a good solid top, say 25mm.
To be honest I'd find making stand for such a little tank a hassle, you could get away with buying a nice coffee table from the OP shop, or a stylish TV stand, or even a nice chest.
I know of no adjustable hinges that can shape the top of the doors(inlay or overly makes no difference in this case) to the shape of a sagging top, and I've fairly extensive experience with Blum and hettich....