My 2 cents:
I've been Unholy all the way, being 78 righ now.
Since you're overgeared for Outland, always kill pack of 6 mobs or so, using your pet as a gatherer or ride by them to pack them. If after a fight you’re low on health, death grip a wandering mob, and then plague it and death strike it, and here you go, full health.
I was going to go Northendre by 70 to be at zone level but eventually went there at 68 and a half, you get brand new decent gear from quests then 1st instances, no prob.
About instances, I’ve always done between 30% up to 40% of group damage since it’s AoE time, according to my Recount.
I haven’t tanked yet, but on my alt “set”, I have now 526 def, wearing tempered/daunting. At 70, I got all the cobalt pieces which I’m sure would have allowed me to tank. Actually, it helped me with some pieces to solo group quests. So far, only the 5 ppl Giant in Dragonblight wasn’t soloable.
Btw, I levelled BS at 70 which I suggest to you to do earlier. It costs a lot and was horrible to farm in Silithus for Oozed Rich Thorium, then in Nagrand for Adamantite, but it worths it now.
Being 78, the Savage Saronite “set” is very good for PvP, going frost presence. At last I understand those Brutal Gladiator going in bg and ripping everyone. I’m not fully used to it yet, but I top the meters (except in AV of course) and I’m very hard to kill. What I like the most is to come back as a ghoul when they eventually got me, then leap at them, stun them if needed and crush them!