Heya!
Are you taking in completely new players aswell and if so is there still active player base running the lower level content. Also what would be the best bet class wise apart from the warlock slot which you mentioned early but that was mostlikely more towards the current raid team so no point aiming for that as a new player :)
Personally been playing on retail since start thou in vanilla only progressed to midway bwl/zg/aq20 and otherwise "wasted" time on rolling multiple alts on different realms and servers.
Atm haven't even made a first character yet since bit torn up if I should start on the fresh server when it comes or on the older one so that when I do get to the point of raiding won't be stuck on purely MC for over half a year(+ zg debuff limit increase )