[Raceboy]

I have installed standalone (VEMS) on 993 '95 (with 55pin Motronic) on the factory harness as Plug'n'Play.
Getting rid of ABD light required feeding pin52 (marked as "PWM" in factory manual) with TPS signal in PWM mode (not analog 0-5V mode). I used boost controller output for that and configured the outout curve just as linear relation to throttle pedal position. Seemed to work fine and no annoying lights.

Can't help you with the immo light other than putting a black tape on it or pulling the bulb
You have to study factory wiring diagrams and experiment a little but my guess is that the immo communicates with the ECU via CAN bus or K-line. Might just buy an immo emulator from ebay for few euros and try.