Welcome to the board Helmut. Bangkok is definitely a lot of fun. I am hoping to spend much more time there on my next trip - maybe 10 or 12 days rather than the day or two arriving and leaving.
My opinion is that it is best not to plan too much. You have a good list to start with, so see how it goes. If you visit a place and feel comfortable there, stay - if not, leave.
It looks like most of your questions have been answered in this thread and there is plenty more elsewhere on this board.
With regard to the health question - this is something that comes up frequently on many boards. I think that you will find many opinions about the safety of this or that. Overall, I think that it is best to do ones own research on this topic - like asking your doctor, calling a clinic, or going to websites that seem legit and knowledgeable in this subject.
My original answer was going to be "use common sense", however I am amazed at the different interpretations of this phrase both at home and especially in Thailand.
Have a great trip!
btw, here are 2 links from CL that might be of interest:
San Francisco City Clinic
and
Safer Sex - s.f. bayarea forums - craigslist