I honestly dont know much about mistweavers but judging from the stat priorities, herbalism probably wouldn't be a bad choice since it gives you an extra haste buff. The crafting professions all seem to be about the same, they equal out to give the same stat bonuses rouhly, though not sure wha tinkers engineering has to offer in MoP
Indeed, your best choices will be two crafting professions. Among these, there aren't really any differences. Blacksmithing, Jewelcrafting, Enchanting, Leatherworking, Alchemy, and Tailoring are all excellent choices. Engineering is also good.
I can say without a doubt for mistweavers (especially starting out in this expac) that Alchemy and Blacksmithing are the best options.
My reasoning is because no other profession will allow you to get that much more spirit (a secondary stat in gems and flasks). Since spirit is so very important for mistweavers, I can't see any other reason for another profession while raiding. These two professions will also translate well when switching to intellect flask/gems, but I don't see that happening for a while.