Emulation (Was: Emulators of Classic Computers)

All this talk about emulators has got my juices flowing again. I use emulators alot, and have always been fascinated with machine emulation. It's always been a desire of mine to code up an emulator of my own for some box but I've never been confident enough in either my coding chops or understanding of really low-level machine details to think I could pull it off (I am an application programmer by day and have done little serious system-level and below coding).

Recently I've been toying with maybe trying to do something, but where to start? I picked a candidate like the Visual 1050 because my first thought was "there's alot of free existing, debugged code that can be utilized" i.e. no need to write a Z80 or 6502 core as there are quality ones available. Being a cpm machine would appear to be another plus in this area. And, I like this machine and I don't believe there is an existing emulator for it.

Now the part that I'm hoping someone who has written an emulator can shed some light on: how much machine docs/specs does one need to hope to have a fair shot at pulling this off successfully? For example, I'm pretty sure that there must be some 6502 ROM code somewhere in that box that provide graphic routines services. If you had a listing of this I'm sure that you'd be that further ahead towards your goal. Or even if you knew where it was mapping into memory you could at least dump it and disassemble it. Thing is, all the docs I have are user guide/usage type things which obviously do not go into these sort of technical details. I'm sure there are those that could reverse engineer the entire machine soup-to-nuts but it certainly seems like that is trying to find the needle in the haystack (which is maybe some of the fun?).