sign up for all programs for starters (BA, United, AA etc); then research the best available routes/rates. Then contact the airline with the best route etc and tell them (don't ask) your plans and that if you choose their airline are there any fast track to elite plans they can offer you. (put the ball in their court). Youre doing alot of int'l flying so the miles will pile up quickly.
FYI - AA is partner of Iberia so that is something to consider, but it also depends what airport is close to you for departure.....
keep us posted.