I think if I were doing this I would start with my speakers and go from there. I'd figure out what sort of sound I like and what dynamics. If my focus were to be with tubes I'd like it if I could find an open baffle (probably) or horn-loaded (depends on your taste) speaker or anything easy to drive. Then a whole world of tube amps, integrated too, opens up to you, and entry level wouldn't cost that much. When you start getting into high power things get more difficult.
