Wow, i didn't expect this many replies
I guess none of the concerns my friends have are valid or deal breakers. Great!
I do however read quite a few people suggesting to start smaller like 250cc. This is actually what i had i mind at first but after getting informed(there are lots of 250cc vs 600cc discussions on the internet) i decided against that and get something with a bit more hp and torque. The parallel twin looks perfect, not a high revving screamer which you constantly need to shift to get in the right rev range.
Regarding a rider's course: As my car driver's license doesn't allow me to drive a motorcycle i will need to get a motorcycle license. Today i passed the theory test
And now i need to follow an 8 hour practical training at a certified center before i can do my exam. After 6 hours i can obtain a temporary driver's license. Then it will be practice, practice, practice. Taking it slowly and not getting too courageous.
In the mean time i started to fall in love with a Thruxton. I realise the upright position of the Bonnie would be better for a beginner. But emotion is winning from reason in this case
The misses wasn't really keen on me getting a motorcycle, but once i showed the Bonnie and Thruxton she's actually excited and is considering to get a motorcycle license herself
I guess showing a friend's BMW 1000RR before showing a Bonnie did the trick
Thanks for the good advice, although i won't go the "smaller bike first"-route it has made me aware that i need to take things slowly.