1. You rank every branch from 1-17. You can then input a "BRADSO," where you commit to a few extra years of service to get a higher preference in that branch. You can also do a "branch detail," where you will do your lieutenant time in one branch, usually combat arms, in exchange for a more...
Very few teams reject people because generally there aren't enough volunteers. Speaking as a sandhurster, I was the only plebe on my team when I joined last year. However, you may not get to compete in the competition if the team has more than the required squad size. Plebes always get cut...
As far as I'm aware USMA doesn't look at your weighted GPA; only unweighted. Colleges in general are considering weighted GPA less and less every year. They do take AP classes into account, however. What's your unweighted GPA?
Its worth noting that you can have a completed USMA application and still be waiting on the ok from DODMERB. USMA admissions knows how slow Army civilians tend to be. I'd bet they'll give you an extension.