Brand new to Star Alliance: all my miles are in US (DM).

I downloaded and printed the *A schedule (all 240 pages!) and there's a lot of interesting routes in there. Before I go all wobbly fantasizing, just what are the rules:

1. If I want to go from, say, city A to city C and the route is A-B-C, what are the restrictions on whose metal I have to fly on? Ideally, of course, I'd like to use whatever carrier was convenient, but I don't believe it could be that loosey-goosey.

2. No matter what carrier(s) I select, I'd have to make the arrangements with US 'cuz that's where my miles are, right?

3. Since US is relatively new to *A (and they have other troubles, too), what has people's experience been so far in working out awards with US res personnel?

Thank you all in advance.