For a crafting profession I would suggest only alchemy until the next profitable transmute (i.e. one with a cd). However, on my first days in cata I sold everything that dropped during questing instantly and leveled alchemy later. If something unknown dropped and I passed a mailbox, I instantly mailed it to my bank alt to put it on the AH.
I sold my first volatile life for 400g per piece (the only one as I put it on the AH). I'm still sure it was an occasion for the buyer. People heading for the server first will pay ANY price.
But they also need stuff that the alchemists transmute, so this will also sell very well. However, personally I believe that the insane prices in the first days will pay so well, that it will be more advisable to sell all material and wait a few days (most people will keep them and level their profession - even more limited supply). Further, in Cata it was good not to go directly to the obvious truegold at lvl 525 as people were more in demand for volatile life (needing lower profession level too - double profit).
Hence, any farming profession will make you rich in these few days. It will be even more insane than for cata, because people like me won't be able to farm herbs as I did in Uldum with my lvl 80 druid alt (big lvl83 mob after me? Ups, let's fly away quickly...).
