Universal Annual Pass
 

I'm looking to purchase 2 annual passes but we aren't heading to Orlando until 2018. If I buy at today's price from the Universal website, are these valid for next year or do I need to wait to January to purchase?

you should verify this with universal, but theoretically vouchers for APs do not expire, so you should be able to buy them now.

BUT, if it puts your mind at ease, you might as well wait until january, keeping fingers crossed they don't raise the price. (I think last time they did raise AP prices was back in august 2016 ... so maybe we're overdue ... )

also check various threads about upgrading to APs
you could also get a 14 days 2 or 3 parks explorer ticket, and have it upgraded when you're there.
some on here report upgrading for $5 ... depending on the AP you want to get,