Where to start?

[MiRai]

Welcome to the jungle...

1. Is there a free program that works good enough for just leveling up?

Probably HotKeyNet, but you will need to learn how to script it. Normally we point new people to this thread which covers a handful of things.

2. Is there a certain class that is the easiest to box to start with?

Ranged classes are generally the easiest to learn with since they don't really require any positioning.

3. Any certain info I need before just trying to hop right into this?

It might depend on the software you end up picking, but I guess a bit of general advice is that you should probably expect multiboxing to be awkward and frustrating while learning how everything works--less so with only two characters, however.