How much paint?

Hello, I'm getting a 1968 Dart 2 door hard top ready for paint. I want to order paint online but don't know how much.

For those of you who have painted their A bodies, how much paint, reducer, hardener should I get?

I want to paint her a Champagne fine metallic (body, door jambs, trunk, etc)

and secondly, should I get a single stage or two stage paint? I have two darts and this one I want to sell, but I also want to do a decent job.

Thank you!