Whitewater doesn't scare me. It's the rocks and trees that are hiding in that water (very common around here) that scare me. That was the demise of Walt Blackadar on the nearby south fork of the Payette. If you don't know who that is, you should, and it should give you pause.
I have a rule about not paddling anything I'm not willing to swim in. Age and injury have resulted in me not being the strong swimmer I once was, so that has me staying out of anything greater than class 3. And even some of that is sketchy.
Some good questions...
I'd say 2+. A 3 was considered, but I chose to line around it.
Capsized, yes. Injured or damaged, no.
I've seen it said that anything less than 3 isn't really whitewater. By that standard, I have never been in whitewater on a solo trip. Neither have I had what I would call formal instruction. I'm unlikely to run anything higher than 2 when solo with a tripping load.