There will be too many problems with any JVM.
1) cmccdll is a very specific wrapper lib. Made just for one project, it doesn't contain all needed wraps for WP. You can use it, but it definitely won't be enough.
This lib is just a very little dll built with coredll7.lib (generated using impdef + lib.exe) and a big .def file using dll-forwarding.
2) No, I don't have API header files, though WM6 ones are valid with some exceptions
3) Dump the ROM and recmod it via OSBuilder (the latter is important, other recmods won't do the job)