1.I would run a radiator without filler cap.
2. + 3. when filling open any valve you have shortly a few times (valve on the heater etc.) Lift the front of car.
4. no other expansion tank needed
5. no idea
I fill my system this way:
Fill the expansion tank, let the engine run a few minutes.
Let the engine cool down for 30 minutes and lift the front of the car. Put it down again and fill more coolant, let the engine run again. I repeat it 2 more times. It is important to put the cap on the expansion tank while the engine is cooling down. If you donīt put it on the coolant will spill out ,it got to be a closed system. Check the hoses or tubes to the radiator when the engine is running, you can feel when the thermostat opens.
Sorry for my English, I am as German as You are.
You can find lots of informationat this Australian website:www.aussieveedubbers.com
forum : non- vw-engine-conversion
Good luck with your new engine.