FreeScale (Motorola spin off) still has 68k manuals and info online for free. Assembler doesn't have very high requirements and your setup is just fine. I use CED and PhxAss also for my assembler. What Piru said but might add...
d0,d1,a0,a1 are scratch registers (contents destroyed) when calling library/device functions on the Amiga.
The absolute memory address 4 contains the location of the exec.library.
