Here’s the project I’ve been working on with the RePhone Create. Fitting the RePhone into a Gameboy case.
Couple of things I wished I could fix - better position of the microphone, and repositioning of the power switch (it’s currently accessable only through the battery hatch.
Full build gallery here http://imgur.com/a/Wj60h
Thanks to the community here for all the advice & suggestions!
Wow, I never thought about fitting the rephone somewhere like that. Now I’m super curious if I could fit it in my Nokia 7110!
And about your project:
A thin plexi or other plastic is way much better to fit the screen, fiberglass pcb materials are hard to work with, they break, etc. I would redo that part, that could save space.
The sound: I would move the mic down to the headphone jack connector, and do you suffer from low speaker volume? The gbc has a lot of space, and a little mono amplifier could be placed anywhere.
And the tricky part: the battery. You should buy 2 AA lithium rechargable batteries (there are many counterfeit, bad ones, beware!) and the trick: don’t even try to connect them in series! Try to move the springs to one side (probably it will end up in soldering) connect them parallell, and voala, you got a really kickass huge battery pack. Don’t worry, even laptop batterries are connected parallell in pairs, it will work.
Last but not least: cool USB connector 
games are evil! 
I’ve spend so much money on cs go…