Acoms
At the start I only read/watch manga/WN/LN/anime with a harem tag in it, I like it very much. But when I stared reading fanfiction, it ruined harem for me. It's just not good, they are full of MC collectors of cumdampster. This is just what I noted in a good harem story. If the MC is a beta male, the harem only needs to be different types/personality. But if he's an alpha, the members not only need to be different types/personality but also different in usefulness/abilities. And harem fanfiction author tends to have an alpha MC, yet only surrounded by many unesesary characters(girls). Alpha doesn't need a useless pretty girls but a beautiful, strong/intelligent and useful women. So your plan is actually good. The MC is eternal so harem is inevitable. In MHA Momo is the best girl for me, beautiful, intelligent and have the most useful ability so she must be the other one. Based on your story the MC will not be on the hero or villain side so he must create an organisation/team for himself and toga and momo is really good for him. Momo is for the logistical support, toga for intelligence gathering and MC will have a self-sufficient organisation. Lastly, I wish this work of yours becomes successful and good luck.