New equpiment!

That's my belief. You just have to be sure that the ball valve restriction doesn't surpass the head height of the pump. In other words, get a pump that matches your overflow or is very slightly above it.

 

Yes

I don't know if HD has acrylic, but I know Lowe's does.

For pump size look at the head data from the manufacturer. It will vary based on the way the pump is made.

 

Hmm. Im looking at marine depot and it seems like a mag drive 7 would be best with a ball valve. But then when you click to put it in your cart it jumps from 5 to 9.5. Im guessing there out of stock but how common is it to find return pumps at an LFS? I could always go to the store to see what they have and while im there check on my phones internet its expected flow at 6 feet of head.