Shellac doesn't have a long shelf life, so ideally it's better to buy the flakes and mix small amounts. That being said, I've always just bought the smallest size can (1/2 pint, I think) that was available at the LHS. You'll generally have a choice of regular or amber; results are fairly predictable and depend on number of coats. I usually do about 3 coats. When it gets too heavy it looks like one of those poly-dipped tables that peaked in the '70s.

I've never wrapped levers, but I bet someone has. Me, I'd rather have rubber there for comfort.