I've got some answers, but not all:
1. Not at the street address level. Tableau can match city, state, zip, msa, etc... but for street address ou'd need your own latitude and longitude and then you can find plenty of examples on how to calculate distances. (for example: Mapping Distances – An Alternate Approach | VizPainter)
2. See #1.
3. Windows will work!
4. I'm not sure what you are asking. Open Street Maps? What exactly do you want to do?
5. You would want to do this outside of Tableau and get a data set that included latitude and longitude which you could then bring back into Tableau. You can find documentation on custom geocoding using Tableau as well as other map related questions.
Can you suggest how can I get geocodes given the address with out much of ambiguity ( errors) . Can you suggest any paid version since the data about customers is confidential and open source would not be safe.
Like any other forum, an informative subject line will go a long way in getting help/answers. "Please help" means nothing because that's why people post in a forum, to get help. Since it's pretty much people volunteering their time many just scan the subject lines and open topics that sound like something they may be able to answer. Posting a question isn't a race so take your time, give details, and use an informative subject line.
Also, I know the improved Search function is difficult to find so here it is:
This can help you with Joshua's suggestion for # 5.