Rotation's fixed. For warriors, there's an optimal opener, the rest's on priority based.
Priority's based on your own judgement. Like what you've mentioned. Better dps skills normally equates higher priority, but that doesn't include something retarded than say, sneaking in a cs in between last 3 hits of boss... it's still up to your own gauging in the end.

Best dps spec for warlock atm is demo. Might wanna use that instead brah.

Was topping on Ragnaros 10 with 21~22k dps for most tries.

Fight dependent. Simcraft Results
Fights like say, Baleroc, it would top without a problem at all. Heavy movement fight like perhaps lord rhyo or even shannox, it sorta suck balls.

It lacks severely for on demand burst tho. Which is something I'm not quite comfortable with. I spent 2 weeks with it, I had my fun, but I think in some sense, affliction and even destro bring more to the table.

As for rag, I'm actually quite apprehensive about how good demo is on that fight. I mean I use to think it's gonna be useful on seed phase for AE, but when I look at the damage meter, it's not actually as much as I thought it'll be. Without felguard, son of flame can't be taken down fast enough neither, which kinda bugs me.

All in all, but to personal preferences on it.