Garrisons look interesting. If you have been out of WoW for several years and are considering coming back, if you've missed the Panda expansion, how is the best way to move forward with toons- level up old toons (is that possible, bypassing the last expansion?) or roll a new L90 toon?
WoD comes with one free character boost to level 90, which will allow you to bypass playing through previous expansions. Newly boosted characters have only a subset of the level 90 abilities, the rest unlock durring the starting quest chain (you can unlock all abilities immediately by swapping specs or queuing for an instance). If you boost a character that is level 60 or higher their professions get boosted also.
Boosting a preexisting character could have a few advantages over boosting a new one. If you did the Argent Tournament durring the Wrath of the Lich King expansion and got yourself a squire with a pony he can still give you remote bank, mail or vendor access, and that is still per toon, not account wide.