just a quick glimpse of your gear says get started in totc10 asap. you'll do just fine as a second tank. what i would suggest tho, is reviewing the beautiful strat videos on this site so you know just what to expect. nothing worse than having to teach a tank how to do a totc10...
start getting your badges, get a new trinket, gemming seems legit.
as far as a guild. if your server is large enough, pug totc, get some gear, maybe get picked up along the way. if you aren't, start apping and building your dps set.
also, ony 10.
as far as 25s, id wait till you are in more 232, health around 35k unbuffed. regardless of what people tell you, ony 25 is not a joke. there is a lot to her and she can hit hard. watch that video too, even if you remember the fight. same for totc25. they hit like trucks.
So get started in 10s asap, learn the nuances and get your meat shield ass back into tanking.
Zeppelin, Wow, and Whiskey... Can life get any better? I submit that it Can NOT!