Okay, first of all, your chances of getting a GV anywhere at seven months are probably slim...but you never know.
If you will definitely need a 3 BR, then reserving at SSR in the 11 month window is a must. And I'd do that early in the 11 month window, because you won't be the only SSRer looking for a GV.
When you do that, the points for that reservation will no longer be available -- they will be encumbered.
If you check OKW availability at 7 months and find it available, be SURE you have MS cancel the SSR ressie first. If you don't, you might run out of points and they would have to borrow from your subsequent use year.
If you cancel, the effect depends on when you canceled. If you cancel prior to 31 days from your scheduled arrival, you would be able to bank 100% of your points if you choose, because your 100% banking deadline is the end of May.
However, if you canceled within 30 days of arrival, your points would go into holding account, and I do not believe they would be bankable, even if you were still within your banking deadline. (I may be wrong about that.) Holding account means that you can only use those points to book reservations 60 days out. That's a pretty serious penalty and one you should try to avoid.