Which professions to choose?

Of course the answer I chose was simple:  All of them!  for those who do not have a stable of alts to allow you access to every profession you have to take a look at a few different factors to decide what professions are best for you.  Personally I pick professions for each of my characters based partially on their class and how that profession will interact with them as they level and what bonuses it continues to provide when they reach max level.  Many raiding guilds suggest if not outright require specific trade skills for each of their raiders based on what benefits are provided by each tradeskill.  For Auction house players the way to look at your professions is actually how they interact.  The best example of inter-playing tradeskills is the ore shuffle.  This first came into place in Wrath where you take Saronite, prospect it for gems, make the gems in into jewelry, disenchant that same jewelry into shards and dust, and lastly make enchanting scrolls with the materials.  To really maximize the ore shuffle, each step of the way you can sell off materials to cover a wide variety of markets.  

Take a long look at what professions your characters have and how they can interact.  I would strongly suggest everyone to make their account self sufficient and have all professions available to yourself.