For the beta test folks who have been in multiple events so far ... does any of the unused event "currency" (milk, tits, points towards mythic cards) carry over to the next event, or do we start from scratch every time?

also does quest progress reset next time cow event come around?

As far as I know, we only had one event thus far? So we don't know till it surfaces. Suffice to say, it'd probably reset that's my guess.

Some users have had two or more events so far.  Not me - like you this was my first event. 

I'd suggest not to reset at least soulstones for the corresponding events. That'll give an opportunity for f2p players to obtain some mythic cards sooner or later.