Good drainage is key, so the tilth of your soil is important. That's typically why you see them planted on slopes or on the top of rock walls.

I'm planting them on flat ground, directly behind 6 inch stone pavers. If they hang over the pavers a little, will that be enough drainage?

Each plant will get around 3' in diameter so keep that in mind. Also, after they bloom, shear them back. I think you would find it really helpful to read the Southern Living Garden Book. It will answer a lot of basic questions.
The library will have it.

I'll plant them 2 inches apart. Thanks for the tip on the book.

2 feet perhaps?

Why plant them two inches apart if each plant grows 3 feet in diameter??!?!?!