For the professions, you really wont benefit from blacksmithing at the early levels. Armor wise you wont get from it and weapon wise you can get those from low level instances.
Once you get into later levels, then you'll get some nice gear from blacksmithing, both armor and weapons. They have some nice level 70 weapons from blacksmithing that shaman (enhancement) can use, not too sure about ele and restro though.
If you are properly funded from a main char, which it seems you have one at a pretty high level, then you can slowly level your blacksmithing if you aren't the type to power level it when you reach higher levels.
For Herb and Alchemy, you'll get some nice potions for hp and mp, also some nice buffs from them too. I'm not too big of a fan of alchemy, I mean the potions and such are nice, but because shamans already have healing spells, reincarnation, and first aid, I'd feel I wont be getting the full benefit from alchemy.
Sorry, from here on I'm going to be talking more about enhancement, because I haven't looked at ele or restro gear. If anyone wishes to talk about ele or restro and how blacksmithing, alchemy, or leatherworking works please do.
I know you're asking about either blacksmithing or alchemy. I'd just like to point out that if you believe you'll be able to get some good weapons once you reach end game, then you might want to look at leatherworking. For leatherworking, there is a very nice 3 piece Netherscale Armor which requires Dragonscale Leatheworking in order to wear it. Very nice gear for an enhancement shaman. Something to think about. This means at early levels you'll be able to make your own armor which is very nice.
Personally I would go towards blacksmithing. Of course I wouldn't mind going both blacksmithing and leatherworking.
The general consensus for weapon speed would be slow/slow weapon. The off hand should be at least the same speed or slower than the main hand. The reason for this is due to the windfury 3 sec cooldown. You don't want your off hand to steal windfury procs from your main hand. So the speed you want for weapons should be AT LEAST 2.4, ideally 2.6 though.
I hope this answers some of your questions, as for dual wielding I don't know what level you get it. I'm leaning towards 41. Since it says you need 30 points in enhancement which doesn't include the 1 point for the talent in order to dual wield. Well if I'm wrong, I fail at math. ^^