You can buy any resort you like, but it is often recommended that you buy something you don't mind staying at if you can't change it at seven months out. It is getting hard to change to a non-home resort at seven months out. Second week of May isn't too hard to book. That's one week we have gotten GFV standard one bedroom a couple of times. If you always plan for May, an April UY would work out good for you. Your UY month is independent on where you can book. It's just when your points start over every year (kind of like a Fiscal year - Disney's is Oct, lots of business have a July Fiscal Year, Federal Government is also Oct 1). You want a UY where you're not always booking in the last three or four months of the year. If you need to cancel 31 days out (to keep points out of Holding), you want to be in the first eight months of your UY to be able to bank them into next year. If you are in the last four months of the UY, you can't bank them and you wind up losing them if you can't use them before the end of the UY.
We have a Sept UY and that works out great for F&W festival visits. Our Dec UY works out good for the Annual Member meeting in early Dec, plus Festival of the Holidays. We don't go summers, so we don't have to worry too much about losing our points.