I have realized that my questions are getting more basic all the time! Feeling more like a beginner than I did when I began.
I have at last understood that the bbpress forum in buddypress is a specific adaptation with considerable feature reductions... and every single forum based upon a group. Further I have realized that bbpress itself is much more capable than this.
So to get specific
1 Can a full bbpress install and the buddypress version coexist?
2 If so how does this need to be set up
3 Does a full bbpress install give multisite capabilities where individual blogs can have their own forums?
4 Is theme integration going to be the nightmare that I suspect that it is (you don't have to answer this, what do you know about my nightmares! But hints might be helpful).