Was told interacting at low level with the animations is a pain(actually, impossible)... there are two ways to do this, one of them is not exposed by Unity3d and would require a custom animation class overriding and interacting directly with the animation framework, this is what I was told is impossible as it is not exposed. (They could always be wrong though)

Unless you mean a 2d fighter, in which case it's cake, just animate the 2d tiles directly, and either use pregenerated animations and switch them, or use a skeleton of sorts (there are 2d skeletons sold in the asset store.

Axis aligned bounding boxes for collisions are easier.

There isn't one for Unity. You need to find someone who is making one and ask them for advice.There's one game called Kinetic Damage made in Unity.

But to start you need to set up animations for the fighting, along with colliders to note the damage, and scripts to affect the health and states.

Tutorials generally focus on tighter subjects. "Making a 3D fighting game" is both overly simplistic in its ambiguity and very complicated in its execution. You should start with simple projects, digging up tutorials for basic concepts and build your knowledge progressively.