I recommend to use at least 2 oz, but you can use less. Me personally, I like to use at least 4 oz of premium bud and a mix of strains. When doing smaller quantities, you just need to be more careful about burning it towards the end of the rice cooker phase. You do not have to use 99% iso. All I have worked with is 99% iso, 200 proof ethyl, and 192 proof polish vodka. The 99% iso was the easiest to work with. The next easiest would be the 200 proof ethyl. The potency is based upon the starting material (buds) and how pure the solvent is. Another factor is not overheating the oil during the final phase. Use a coffee mug warmer, very important.