I was going to touch on the % aswell. I use 99% proof.. If could get 100% i would use that. Every grow shop i have been in has had ISO.. I would avoid going to the drug store. I paid $25 for a 4ltr jug of it.. Which has lasted me 2 years easy.
I have, and still use a double boiler. It's very safe, i also recommend using that method.
The difference with cold extraction are the terps, when you boil it you can evap your terps pretty easy.
Not many people know you are also boiling away your terps with the ISO. The end "strength" of the product is the same, but if you like some flavor to your oil room temp evap is the only way to go.