With regard to stretching: the amount and chance of possible stretching in a single session is currently alright, but tightening is kind of an issue.
1. It happens way too fast. I spent a week trying to stretch Cali enough that I could fuck her without risking tearing, but gave up because she was tightening at least as fast as I was building up stretch.
2. Minimum tightness is a bit too low, particularly on vaginas. Seems like 90% of characters have a minimum (which due to the above problem they're nearly always at) of "tiny," no matter their age. Adults shouldn't naturally tighten below average once stretched past it, and teens should only have a chance of doing so