I'm assuming your looking at June of 2015 so you've already made your reservation at your home resort with your points available and that you may or may not be looking to change to another DVC resort at 7 months. If so, your first and best bet is to borrow your own points even if it leaves you short later, you're second best option is to get points transferred in and the directly rental of 24 or less is last. It's possible you won't find anyone to do simply 4 points so if you chose a transfer you'll need to get more for later.
Unfortunately, you don't. Buying one time use points can only be done via live phone conversation. You have to give a credit card number to them and they will process the transaction and get your room reservation in the same call. Straightforward, but not ideal if you're trying to snag a high demand reservation that might fill up between 8-9am when MS opens.
Borrowing points from your next use year can easily be accomplished online. You just start to reserve an accommodation that is more points than you have in a given UY, and the system will automatically prompt you to borrow from the next UY to complete the reservation.