a meh geared holy priest can cheese farm diremaul plants for 40g ish an hourNo. Prot Warriors will always be in demand. Guilds need 8 geared tanks in Naxx40 for 4HM. You may have trouble finding a spot as a DPS warrior because they will almost assuredly be the most common spec at 60, but Prot Warriors (or 31/5/15 Warriors who don't mind tanking) are always in demand.
It was very spammy. You needed to stance dance at times for Fears. You have extremely limited AoE threat tools so tab targeting intelligently is a must. Gearing is kind of obnoxious because you need several different kinds of gear for different situations (Resist, Threat, Max EH).
Yes. I would advise all main spec tanks/healers to roll a Hunter/Lock/Mage to farm with. Unless you're an AH wizard, respeccing to farm is not really an option, nor is farming as Prot/Holy/Resto. Your only other option is farming in groups and 5mans (less efficient) or just gathering professions. Legit options, but not as good in the long run as a Hunter/Lock/Mage efficiently farming.