So hey, I have a question regarding some units, I noticed some units have stat like the Demonic Obelisk from the Thrall of the Formless One set. It has 0 for all of it's defense stats but has a (6) underneath. What does that mean? It gets those in favored terrain or is there something else I'm missing? I've noticed this with other units too.

Yeah, absolutely! play with all 50 tiles and build from the center-out. Once it's built, place bases so they're at least 5 tiles away from one another. That should about do it.

Can I play whit 5 friends using the same rules but whit one bigger map?

When you make a melee assault, you move into an adjacent tile. Arcane and Tech (the abilities you'll find in the third slot) can be used in either way.