You can never have too many gifts if they don't change the affection scaling... I already managed to burn thousands of gifts on just a few girls. I spent 150 million on pachinko since the update and I'm running out of gifts already. There is no income stable enough to handle that, and every additional girl is more expensive than the last...
You are spending about 2x what you would pay for the same items from the shop at that point, and that is only if you sell everything else back... It takes a lot of time even if you do sell equipment back, so it's kinda bothersome...