August is my use year. If I were to add on points, but the use year is October, can I still book 11 months out based on the August use year?
1) use year has nothing to do with when you can book. zero. nothing at all.
2) technically, you can't "add-on" with a different use year. if you have a different use year, you would have two master contracts - i.e. you'd have to buy a new contract or a resale.
having 2 master contracts means if you book a resort at 7 months out for one night, you cannot combine pts from both contracts without transferring pts from one to the other.
And what if the points were for a different resort?
home resort dictates when you can call to book. if it's a different resort, you'd have to wait till 7 months out to use those pts at your first/master home resort.
If I needed 200 points, 150 from August UY resort and 50 from October UY resort, would I be able to book 11 months out from the August UY but using both sets of points?
if they are both the same home resort, yes, you can book 11 months out (again, use year doesn't matter). you would have to transfer pts between the contracts to pool points to book a single night...or else book 5 nights with one contract and a separate reservation for 2 nights with the next (or whatever) and then ask MS to link those separate reservations.
IMO, yes it's a hassle.
OTOH, if you usually travel at different times of the year...it might be helpful to have 2 banking windows. but it is definitely more to keep track of.