You asked about rear derailleurs and cassettte compatibility. I am running a 13-29 on my climbing bike with a short-cage derailleuer. So, you can probably go much bigger in the back with little problem.

With a compact 50-34 and my 13-29 cassette, I have gearing VERY similar to a triple, with little weight penalty. I have this on a bike that I'm setting up strictly for climbing rides. I have a 12-15 for flatter routes.