I've been using a mk3 style coil and ignition amp on my 9a for several years without a problem, it came off an audi 80 16v though so may be slightly different in some way though. (Must go and put a spare in the boot in case I've just cursed it)
I gave my rev counter a signal directly off the trigger terminal on the coil, which is how older cars factory and aftermarket rev counters worked anyway. I didn't find an easy way to make it work with the ECU feed that my donor Corrado used. I think the ABF works the same way. As for the other wiring like warning lights and temp gauge, I think you can just splice the rocco's wiring to the ABF loom. I'm fairly sure the sender and gauge are the correct range and calibration for each other.
Rubjonny over on clubGTI
has links to various wiring diagrams in his signature, as well as creating the fusebox FAQs which were invaluable to me when working out which wire on the fusebox connector did what.
Edited to add link.