I am currently in the process of making something similar.
The difficulties I am having is that space is very tight in the case when you add slim CD/DVD if you are going to run IDE-splitter so I may go without one.
Anyway, what I have planned to have in my A1200,
BPPC with BVision
DCE-FF
CF or 2.5 HD
Slim DVD
IDEfix
Floppy
Bmon monitor switch
Internal mounted wireless NIC
+ lots of fans
