Not sure I know all the answers, but I'll share what I do.
1) Yes. Relatively new, but redeemed nights do now count toward maintaining status.
2) Yes. Platinum arrival points as well as ports for additional spending (depending on the brand).
3) Most members like to get a USD value of $0.01 per point (i.e. 25k points redemption at $250 or more). Other factors might be considered (current points balance, ongoing promotions, etc.)
4) Not sure. I've never tried to use points for anything other than the room rate. Some places will let you earn points for parking, other not. I know there are some ways you can use points for things other than the room rate, but if I recall, in general the value is not very good.
I have no doubt others will chime in with additional comments (and corrections if I misstated anything).