There are possibly several issues here.
The numbness of which you speak may be caused by pressure on the perineum, and is fairly well-known. Saddles with a gap in the middle are supposed to help, as is tilting the saddle forward slightly.
In regards to general chill, then simply layer up.
In regards to chaffing, that's simply a mechanical issue, and I find it's worse when wet.
If I ride a shorter distance wearing underpants, if they get wet, I will chafe.
I'd not wear underwear on a longer ride. (!)
So avoid your little cotton panties.
Apply lots of cream, esp. if it's wet or cold.
I just use the left-over sudocream from when our kids were babies!
It also seems to me that the chafing is related to the hairyness, and that hair acts as a grinding agent.
I've considered ( but not yet tried ) a bit of judicious shaving in the affected areas.