Back plate braces: you don't really need a dish. Takes a look here:
http://www.hoffmanguitars.com/back1-111.jpg
http://www.hoffmanguitars.com/bkjg-50.jpg
As for the top, make the guitar flat unless you really need it dished. And one other thing about dishing the top -you'll have to cut a concave hollow under the bridge to match the radius of the top. This hollow will have to be quite exact for maximum energy transfer from the strings to the top.
Go through the rest of Hoffman's site - he has built zillions of guitars and is a master luither.