Yeah...harem will work out totally fine...until he subconsciously makes a decision, whom he likes most or has the feeling, he has to spend more time this some waifu, because she needs it and the other waifus feel unloved or not as special. Honestly, if I can imaging some harems working, then some with an hierarchy and based on interests, like money or social standing, but not one, that is solemnly build on (falling in) love. The first heartbreaks and drama will surly follow. Or he manages to spend his time in a way every girl doesn't feel left behind, which I imagine isn't fun and only works, if he kills off his heart. 😋 And then he will have an extra-marital affair anyways. With a girl, whom he fall in love with, because everything with her is so much simpler, he feels free while being with her and can be himself again.
He should just chose the bookworm girl, because she was the first (not ghost) one and see if it works out. The end.