10oz injector? That thing must be huge.
I suggest you try the different salts and see what your preference is, any of them will work.
Microwave will be more than fine. You only need a pot if you plan on doing larger production runs.
I stir with a cheap butter knife, its flat on both sides which makes it easier to wipe off excess plastic.
Make sure you have at least two Pyrex or Ancor measuring cups to heat up the plastic in.