[@floodtalon]

1)
If he leaves a body of his own free will, he can keep going pretty much as long as he pleases. If a body he occupies is destroyed twice in rapid succession that's enough to boot him off. This means he'll usually retreat after he loses a body, depending on how badly he wants to win the fight he's in. If he takes a full post or so to rest between destructions and nobody interrupts him he should be able to keep going. No damage to his mental state is permanent, so it's important to strike while the iron is hot. Other attacks that contribute to the mental strain would of course also be a factor, such as destroying his deployed spirits or performing mental attacks.

2)
will do.

3)
To me, any attack whom's target is the physical body would be a physical attack. A laser beam's goal is to disrupt materials by flash-heating them, the damaging factor is heating physical matter rapidly. As such it's a physical attack. Nonphysical attacks would be things like soul-destroying spells, psychic assaults, stuff like that. A Machina with dedicated ghostbusters technology could certainly affect his incorporeal form, and something like the Reality Breaker would definitely work. But something like a standard Machina laser beam is going to go straight through him.

4)
I was planning on putting that in there, but forgot. Most Machina technology would be shielded in some way. He could use machina scrap to create a scrap golem, but not possess an active mech suit or something similar. Especially sentient ones.