MC gonna have to level with them and say that that's a lot to take in at once and that he needs to have some time to think.
As far as harem manga MC go, this MC is one of the few I could actually see doing that instead of just running away screaming.
Either that or he could tell them that there's a ghost that's as old as time following him around telling him to knock chicks up. That should weed out a few of the suitors.