Crafting should be started early in my opinion. I do the quests while I'm in the world where I get it. It's not really all that useful until Wintertusk, but it really helps a LOT when you get to level 56. Coincidentally this is also the level when Bazaar gear starts to become completely worthless. If you wait to do the crafting quests until you need them, it will take you about a week because of cooldown timers. That's why I say do them as you go because then the timers don't matter when it finally comes time to really craft the good stuff.
I don't craft the spells so I use my main wizard which is Life as my crafting wizard. She has crafted all 7 sets of the Wintertusk gear sans some school boots that didn't seem worth it. As new wizards turn 56 they get this gear slapped on them. I am also going to work on crafting up the Olympus gear that I have gather on another high level wizard to craft the regular Senator gear to the next level for all schools.
I do the crafting quests though the Seal of the Seven Seas on all my wizards just as something on the side to do as a game diversion.
Crafting isn't necessary but it does help to be able to do it if you find something you would like to craft. On my Life wizard when designing her palace I crafted a few furniture items I had wanted too so it doesn't always have to be for gear or spells.
As Seethe42 said though, it is best to do the quests a long the way. I always begin and end them in the world given before I leave that world. Since I collect a lot on my way and have quite a stock pile of rare stuff or stuff that can be transmuted into rare stuff the quests are actually easier for me. Once you learn the ins and outs it actually can be done in a reasonable amount of time.
Crafting is not that good at the start but should be started. Later once you get around level 56 (level 56 gear) it can become a great help. And later when the hat and shoes are better that. hades gear, yes its very inportant