2) There isn't a good optimizing C compiler for 68k. Vbcc is comming along but it's a huge project to make a crossplatform multi-CPU C compiler. GCC has generated some horrible code and some of the newer versions have gotten worse. Many C developers don't even know when their code runs at 1/2 speed. This is more common than you think.
Sidewinder and I have been trying to drum up support for LLVM on the 68k Amiga. If the 68k backend is completed, the Clang compiler would be available for the Amiga. The catch is that it is mostly written in C++ and the backend is written mostly in a utility called TableGen.
The closest backend to the 68k would be the Intel x86 series. It would need to be stripped down to the bare minimum also since 68k doesn't support vector registers.
I expect when we start the 68k backend we'll probably use VASM as our assembler unless we need JIT support. We will need to render code directly to RAM if we do that.
Keep in touch, Matthey! We'll need to have all the help we can get.