I too is the in the same boat mate, To power the me3.8.3 you would need the following (this is my setup) a power supply unit I used the one out of my old computer, a MPPS lead (ebay special) and some sort of crocodile clips.

Note: If you was to use an old power supply unit (PSU) you would need to jump the actual unit on most PSU it's the Green and black wire touching to actually power the PSU up

I've posted the ME3.8.3 diagram

That's all I have so far mate

m3.8.3 is a bit a pain because you cannot read it over odb. Some ecu's you can write over odb, it depends what revision they are.

See this threadhttp://nefariousmotorsports.com/forum/index.php?topic=8568.0title=

there is a big thread on m3.8.3 tuning, search and you'll find it.

Typically M383 uses AM29F200 PSOP44 flash eeproms. You can desolder it to take OEM file, or you can check it using ID procedure with MPPS  and look for OEM file in the net.

The one you prefer. It does not matter as long as you are able to apply changes properly and then to recalculate checksum.

If you want to stay legal and do not spend huge money on software your options are pretty limited - TunerPro or just any free hex editor. Checksum could be solved also using free tools but it depends on which exact ECU are we talking about.