To answer your specific questions:
1) Probably a good idea
2) "linux" is really just the kernel, a "linux distribution" contains a lot more (filesystem, applications, UIs, etc). Embedded linux is generally stripped down to essentials.
3) Not too detailed, but it definitely helps to have a good foundation
4) Microblaze is a target architecture for the linux kernel, which certainly will make things easier for you, but there may be minimal to massive amounts of work depending on the device you're targeting
5) No, you have to use the correct toolchain (C library, compiler version) for the target board.