1. Currently, Wuelie is the only girl from whom semen is available. Semen from other girls will be added in the future.
2. Sorry, i think it's a bug. If you write that down in detail I may be able to fix it.
3. the mushroom dog is back where it belongs. Once you enter the Catera's house, the position is reset and relocated.
4. you cannot get that achievement after defeating the boss. So please try that with a new save data.