1. Yes; note you will need to connect someplace for LAS-BOS (DWF, ORD etc.) as there's no nonstop and that would constitute a second N. America transcon anyway, which is forbidden.

2. Define "improve." More miles? Nicer flights? For example, most folks would say that the nicest transcon in N. America is CX's YVR-JFK or v.v. Not a lot more miles, but definitely an "improvement" as far as I'm concerned. YMMV.

3. No, call the RTW desk and they will queue it to Dublin for pricing. Or you can use AA's GSA in Sweden, TAL Aviation (search or google for contact info.)

4. Yes.

4a. Yes.

5. Yes, all but the first.