One advantage of rampant altitis is having most trade skills covered. This enables efficient use of almost any materials and much less wastage while levelling up.
My highest level characters are generally equipped as gatherers. They farm materials while I level up and mail them on to the trade skill alt. Crafted materials are made up and then either mailed to the banker alts, or passed on to another alt for more crafting.
Cryptography my "main" rogue is a skinner and leather worker. I've kept up the skinning but LW has lagged behind. Occasionally I'll make a bit of effort to get it going again but usually find some other distraction. Mostly the leathers are sold on the markets. I have considered dropping LW on several occasions but have resisted so far.
My new Death knight Cryptoknight is a herbalist and enchanter. This is my main farming character at the moment since AOE farming of low level areas is supremely awesome. He uses the enchanting almost exclusively for disenchanting of BoP items in instances. Herbalism is still quite low but is progressing and every one of the mats found is passed on to another alt for use. Excess enchanting mats are passed on to the banker for resale.
Mortified is my primary bank alt. She's now a level 35 mage, so has increased her maximum trade skills to 300. Enchanting is the main priority at the moment. She disenchants almost everything that gets sent to her from other characters and sources hundreds of items each auction session. She is also an accomplished tailor. Both tailoring and enchanting were level capped at 225 for a long time but now have room for expansion. Tailoring provides gear for my cloth wearing alts and also supplies market and disenchanting opportunities. Eventually I'll have to get her out and questing for more levels to keep up.
Afterdeath is a lowbie priest. She was originally herbalism and alchemy but has dropped herbalism in favour of inscription. Eventually I'll have to get some her some levels but for now I am well below the level cap on either trade. Herbs are supplied by Cryptoknight then used in either inscription or herbalism. Inscription is starting to supply decent glyphs for my alt army or for guild use but is also making lots of weapon and armour vellums for my enchanters. I do not use a lot of potions on any alt and those that I do use are higher skill ones.
Rigormortis my warlock blacksmith and miner has been transferred off the server. He is now the highest level alt on his new realm and may end up dropping the blacksmith in favour of enchanting or something. He used to supply reasonable green and blue items to my lower level alts, or supplies for disenchanting. Mining of course is always financially rewarding in the AH.
Decrypted is a miner/blacksmith. Both of these have been neglected since Rig did most of the work. He's also a warrior and probably the least likely alt to be properly played any time soon. When I originally planned out the trades, he was going to be an armour smith to complement Rig's Sword smithing. Not sure which way he will go though I do have three plate-wearers now.
Ashnazg my Paladin is also a neglected character. Mining and jewelcraft are his token efforts. One day I might actually spend some time getting this guy levelled up since AOE farming is so fun on the Death knight! When and if I do, Ash will add further to his current trade skills.
Methane my druid gets an occasional workout. He is purely a gathering character with skinning and mining as professions. Most of his output has been passed on to my lesser leveled alts. I chose to make him a dual gatherer becasue druids are so versatile. Stealth in cat form, travel form, swimming form and flight forms all make for a character that can get to places easily.
Insolence is a blood elf warlock. I originally had jewelcraft and mining but dropped jewlcraft for herbalism a while before wrath was released. Now that Cryptoknight has much better herbalism I am considering going back to jewelcraft! Either way, she is my primary non-enchanter bank alt and doesnt get much sun at the moment. Jewelcraft generated a lot of enchanting materials but there are many other low level jewelcrafters producing rings and necklaces so theres not a lot of profit at the low end.
Cyanade the shaman is a skinner and leatherworker. For a long time I was passing scraps to her from Crypto's lower level adventures, so her leatherworking skill isnt too bad for the amount of play she gets! Back in the day I had planned that my two leatherworkers would specialise in one of the three types but that is still a long way off if it ever happens!
Last but definately not least is Kytlin, a hunter just barely short of level 50. Mining and engineering are her professions. Both are lagging behind where they should be, mostly becasue being a hunter is so much fun I forget to mine! Engineering so far has just been a massive gold and materials sink with very little to show for it. I have the gnomish remote control trinket that is supposed to be good on mechanicals... but I cant even remeber trying it out!
Anyway, the synchronicity part of this is the several chains of supply that I can have between my characters.
A fair few quests require crafted items. In theory, my alt army has been able to supply most of these... but in practice, the AH has been too tempting. Alchemy, Blacksmithing and Engineering crafted goods are the ones most often needed in quests. Be aware that the quest rewards are often worth a lot less than the cost of the crafted items!
Most craft skills can make objects that fuel the enchantment market. A large proportion of tradeskill gear gets consumed this way. If you are not an enchanter, be sure to price your junk greens on the AH at a price that is attractive for disenchantment. Blue gear is rarely worthwhile either to craft for sale, or for disenchantment.
My current best chain of recycled crafts is this: Herbalist farms herbs. Inscriber mills them for ink, then makes weapon or armor vellum. Enchanter uses farmed enchanting mats to place enchantments on the vellums, which then are passed on to other alts for use or resale. If everything works out I could get 4-5 skillpoints on three characters from the same stack of herbs!