If you stuck with all 3 species being the smallest available sizes, I think it would be safe "size-wise", i.e. 3"-5" SMB should not be eating and 2"-3" YP & RES. Just FHM, like you say.
Whether this is wise from an out-year perspective, wrt when the different species start spawning, I'd like to hear from Bill Cody or one of the other YP/SMB experts.
Until then, review Brettski's
Help me adopt my fish family (he was looking for character references), paying attention to discussion leading to the ultimate RES/YP/SMB decisoon and paying particular attention to Bill Cody's posts.