Your best bet is the Alumilite Clear. It is a formulation I helped them develope specifically for turning. It has better polishiability
As for how many blanks...depends on the size of blanks. Figure your size in cubic inches (length x wid x height) and multiply by .554 and that will give you aprox how much resin you will need. There is 128 ounces in a gallon so you can do the math from there.