When you open toribash it's classic by default.. is there a way to set it to "gravity 0 0 -30" or "sambo.tbm"? Which file would I have to modify to do that?

You just need to go to setup/option and check the remember game rules.
Then you go single player, modify what you want and exit

When you'll get in again, single player will be the way you want it.

the only problem with that its that you cant set mods with objects.

I don't see why couldn't you.
Just set the mode then exit, next time you open toribash, it should be with that mod.