'Ignition Setup'
I keep distributor only for distribution. I use Hall sensor on crank as a trigger input for the VEMS.
Q: So actually I have to lock the plate in the distributor and remove the vacuumline in order to lock the vacuumadvance and let the distributor only distribute the spark?
A: With the distributor used only for spark distribution, and not timing advance, none of what you described is necessary. The poles in the rotor cap are fixed, that is all that matters for spark distribution.
Q: Do I need a triggerwheel or can I just bolt on two magnets 180° separate on the standardcrankwheel?
A: With many auxiliary belts (air conditioner, servo steering, ..) this can be a problem to fit correctly. The main concern is that it must be rock solid and accurate, and be appropriate for the sensor you will use with the trigger solution. With a good Hall trigger (Honeywell GT1 is recommended) you don't have to use magnets, two slots or fields in a ferrous material is all that is needed and can be fastened in many ways depending on how the stock crank pulley is designed. In this day and age of cheap digital cameras, pictures still speak more than a thousand words, so get some snapshots.
OK here is a pic from the crankpulley:
TODO: fabricate trigger setup with Hall sensor on original crankpulley