i wish you best of luck with your project. just some remarks if i may
1. don't go for TTL. Search for analog for all your modules. You will get bored of TTl very quickly (in an RGB it gives only 7 colours, while analog is pretty much unlimited)
2. don't start looking for a case yet. measure all your components making provisions for red and green, get a 10mm thick alu plate, bolt everything up (ideally optics and lasers top side and all electronics at the botom) and then build a case around it. Ok, the "bolt everything up" is oversimplified, you will have to work out wiring and grounding schemes
3. not sure why you want pbs instead of dichroic filters to combine the colours
in general, search PL photo gallery to see other peoples' builds. you will get some very usefull ideas. even some peoples' avatars can give you many usefull hints
in any case, best of luck with your build and have lots of fun. don't hesitate to come back with questions
ps. don't forget to fill the "location" part in your profile, so people will know where you are
"its called character briggs..."