Is this a subscription service? Or do I have to purchase this data each year?

It's a 1 time fee, not a subscription. And for that 1 time fee, you get the most current Census demographics available at this time.

Do I get updates as new data are released?

Next year's data isn't included in the price of this year's dataset, and you could choose to buy next year's data when it's available (typically in December).