I paid 17$ each for Vampires, drove through a snow storm to get them, I didn't know they were that territorial or I would have only got one.
Shrimp are Shrimp, you generally don't have to worry about any disease like ich. I'ld buy them from a tank that was infested with ich.. doesn't bug me one bit.
I have a Fluval 304 and a Maxi1200 going through a filter/reactor setup. The current is far more then you need, if there is no particulate in the water they will rub their fans on the rocks to pick up food.
Vampires defend themselves 3 ways depending on the fish that I've observed.
1) fan poke, the fish usually leaves it alone.
2) spike poke, They have a spike where the claw would be. This can be lethal depnding on where it hits (eye, spine (it got a cochu which was terrorizing it there) or head in general)
3) Maul, it will wrap it's front legs around the fish/shrimp and keep hitting it with the spikes. this is how it killed my bamboo. very efficient at it to, similar to a cat wrapping their front paws around your arm and tearing at your arm with their rear legs.