I triple box... have one full set of 80's and am now using one of them to assist two of my 70s to level up.

Back when I had 5x70 toons, I would take prot pally, holy priest, and arcane mage through all the island dailies, then swap out rogue and boomkin (keeping the mage in) and run the island with them. Just doing that, I made like 500g a day.

I honestly haven't dug that deeply into the Northrend dailies yet as I've decided that I want to level up my rogue and druid.

As far as the economy goes, I used to do quite well watching trends in pricing and then farming up/pulling from bank alts stuff that was currenly highly valued and just holding on to stuff that was in a down-cycle. If you get a good handle on your realm's economy, you can often spot trends in certain items so you can implement economics 101: BUY LOW, SELL HIGH.

The whole thing with trade skills is that WOW is often very "upside down" on raw materials versus finished goods. With the exception of stuff with CDs (tailoring, transmutes, etc) you often find that the demand for the raw stuff is high cuz other folks are trying to level their tradeskills.

I find that unless I'm going for a specific tradeskill item (say, farming tons of Saronite so I can level my engineering on one toon) farming for mats feels too much like "the ultimate collection quest" which as a multiboxer, I just have to hate... it's in the rules, isn't it? . Instead, I try to just take my time leveling and farm out the mats while I go, or farm mats while doing dailes once I finish leveling my "b" team.