What defense are you running?
I'd lean towards ATH/SPD/PASS being a focus. I think having big men who can pass is a nice bonus in the motion offense. That and don't follow my example at Texas, San Antonio in Smith. My team's prestige is poor enough that recruiting to the offense is almost impossible. I just pick up what talent I can find; but I have had success with motion offenses at DIII.
I'd say I rely more on outside shooters, but that's just me. The motion offense tends (from what I know of it), to be focus slightly more on the outside game. That doesn't mean you shouldn't get bigs who can dominate inside, it just means that maybe you should have a little more depth at guard than at forward/center.
And you don't have to necessarily follow that advice. I just tend to take ATH/SPD/PASS/PER to be most important in a motion offense. By switching my old DIII Frostburg State team in Smith from a Fastbreak (I think) offense to a Motion offense and recruiting big time ATH/SPD/PASS players, my team went from DIII doormat to DIII powerhouse in just two seasons.
I don't know if the same success is possible at DI, but who knows?