So, correct me if I'm wrong, but it seems as though Affection doesn't need to be maxed on the parent cards before Training occurs, as it simply transfers directly to the new card, but doesn't actually raise the ceiling affection of the new card. IE: If I put two Common cards with max affection through training, I get 40/100 affection on the new card, but if I put two Common cards with only half (10 affection each) then I get a card with 20/100 affection. Just thought I'd put this observation out there, as it will really help to speed up my Training process. Again, this is just what I'm seeing from my own experimentation, so please feel free to correct me if I'm mistaken, and I'll edit my post.
^Just to confirm, I still max-level the parent cards, as this does affect the final stats of the new card, but you don't have to max-affection them (so it seems). Any affection that you do gain on either or both of the parent cards will be directly transferred to the new card (therefore you are never "wasting" affection gained on cards that you plan to use for Training).