Well, I'd need to know what you have in mind exactly, before commenting on it. I allow patrons that go for the 25$ tier to suggest one scene, for example, so I am not against all input, but I keep my right to veto stuff (as an example, I don't like vore or anything of the sort, so I don't want that in the game).
It would be similar for adding a character. I'd need to know what the character would look like, what's their concept and what would they do, and how much presence do you expect them to have in the game. If it's just a minor NPC with one scene, as long as the character looks good I wouldn't be troubled, but I might have to reject a big undertaking at this point in time (as I get closer to finishing the game, I have to focus more on the "to-do" list, rather than on adding new stuff).
As for helping, I currently have enough testers, but if you have more suggestions as you play through the game, share them with me. I can't make promises I'll work on all suggestions (some things can take too much time or I might simply disagree on what's best for the game), but I try to hear anyone who's interested in improving the game.