Gurneys is having a sale on blueberries right now and I'm wondering...how big do blueberry bushes get? I've never gone picking before and don't know a thing about them...but would love to have some bushes.

What kind of sun do they need...are they messy? Do animals eat them??

You would probably want to plant highbush blueberries. They get to be about 6 feet tall under cultivation with proper pruning. (prune out all stems over 4 years old as the younger stems are more productive) They will get much taller in the wild as wild plants are unpruned.
Blueberries need full sun for best yields. I mulch mine with pine needles as they like a pretty acid soil. I also mixed peat moss in the planting holes. Birds love blueberries and you will need to cover your plants with netting if you expect to get a decent harvest. Blueberries aren't ripe when they first turn blue. Wait to pick until they pull off the stem with very little effort for fresh eating. For jam and pies though, I pick all berries that are fully blue as the tartness of the immature berries give better depth of flavor. Fertilize in spring with cottonseed meal or Holly-Tone.