all the girls you get you should get max affection. it gives you more cash at a greater time frame for collection.

level only matter for the girls you use to fight with so you don't need to level any other girls but the 3 you use.

the great pachinko is the best way to collect a stock pile of EXP items and affection items.

my advice is keep every book!

keep only the green level panties after you have at least 40 of them sell the rest.

also as for gear only use gear that improves the trait you are anything else does nothing for you only leveling the trait you are makes any difference to your ego.