Hey lvl 23 here, so far I can tell you:

- XP is not really important, bosses are really weak and you really only need to max your alpha to get bigger ego.

- Later on you will have LOTS of money and nothing to do with it, when you're out of books or gifts just go play the pachinko with the 10 games button it's worth it.

I have 12 girls with max affection and 3 at max lvl. Hope that helps.