Just a word of advice on the harem and romance. From my perspective (pagan and poly), the key aspects to a successful harem are twofold: First you have to be so in love with the characters that you want to share your life with them and can't give them up even though you have other deep relationships, and second the women involved must be willing to share you and must be able to get along. Pumping up the romance is the best way to get that emotional commitment. Let us find out more information about each major love interest, and it speeds the processif the character has a problem or a trauma that the main character can help her overcome. In the end I'll want her in the harem not only because I love her, but also because it will protect her and help her become a better person (heal her trauma). That emotional commitment lifts a harem game from a three star pokemon (gotta get them all) to a five star classic.
As for why they would choose to share you, there are a couple of routes you can go. The girls can be so in love with you (or your magic dick/supernatural power) that they don't care how many other women you have as long as they can tap you (not very romantic). The girls may be attracted to each other and be willing to share a true polyamory relationship (this will require some interactions between your harem members and the development of a relationship between them). They can have a sisterly relationship (best friends sharing), but not a regular sexual relationship (the sister wife concept as practiced by some polygamous sects). Alternatively it might be a cultural norm with established roles (First wife, second wife, junior wives and consorts). Harems don't just fall into place (unfortunately), they need some effort to build.
Some people just want pokemon sex dolls and a quick fap, and there is nothing wrong with that, but I suspect those folks are less likely to be the long term supporters of a project. Give us a relatable MC who isn't a douche, solid development of relationships between the characters, and believable reasons why you end up the Harem King with four or five women sharing your household and your life, and you'll get some long term support and a high rating. Yes, this turns the MC into a bit of a White Knight, but from my perspective there's nothing wrong with that. The Goddess is in every woman and all acts of love and pleasure are Her rituals.