Sounds like a great trip.
I've always paid cash for the rental cars because point valuation was never so good; using the Alaska/Delta points for flights will often get better $/pt.
Last year in Europe we rented 5 or 6 cars with fairly good daily rates. The key was looking at 1-way fees and cross-country fees. For example, driving from Austria to Italy caused the price of the rental car to triple, so we returned car1 in Innsbruck, took the train to Bolzano, and then picked up car2.