What medium to use?, Soda, Sand, Walnut, Plastic, etc. Options

[Poor-sche Lover]

I have recently gained access to a high quality sandblaster, but I really don't know much about the process. I have a few questions.

1) Do I have to use sand for the blaster, or can I use something else in it? I've heard that you can't use soda because of the way it feeds into the system?

2) I want to use soda because it's less abrasive, but I read that soda will not remove the rust. I definitely need to remove the rust. Which type of medium is best for this?

3) Can you give me any general advantages/disadvantages of soda, sand, walnut, or plastic? Any others that I don't know about?

Any advice/suggestions/info you could provide would be helpful. Nobody around really does this, so farming it out isn't a viable option. It's either this or the long way, and I'd really like to blast if I can. Thanks for your help, guys.