Welcome to tanking! I am a recent prot warrior respecc, lvl 67, and pretty new to Wow too (/played = 14 days).
I agree with the above posters.
I respecced when I hit the early Outland instances (Ramps / BF / SP), and still run them for the experience. I'm over-levelled now, which gives me greater margin for error while I improve. Better to cut your teeth - and make your noob mistakes - on regular 5 mans, I think. By the time you're in Kara the expectations will be higher, as will the skill level.
Learning to tank is not just about what you can do, but also the capabilities of the other classes. Between not knowing the instances (first time in), not sufficiently appreciating how group composition (eg presence/absence of CC/rogues/casters/offtanks) affects strategy, and not having my own responsibilities committed to muscle memory meant for a couple nasty, failed attempts. No doubt I'm on the /ignore list of some of the less noob-tolerant players I pugg'ed with.
Just forewarn your mates, develop a tough skin, and have fun!
To your questions:
Charge v pull: Pull if there is a risk of aggro'ing in other mob groups. Otherwise charge, and move the mobs back to an area safe from other groups / pats.
Multimobs: Generally, your combat sequence makes sense, except:
(i) You should be in Defensive Stance, not Battle.
(ii) Better/easier/faster to apply Devs on the non-Skull mobs rather than SS (cooldown, rage cost).
Keeping up shield block is battle-specific.
Do keep your shouts up if you have the rage.
Unlike Dev, Sunder can be used to build threat on CC'd mobs, without breaking control. But except for this special case, use Dev.