When to start leveling my professions

When should I start leveling my professions?
Should I do it when I have all of my teams?
Or should I do it as I am leveling up from RAF to 60?
I'm unsure on how best to select my professions for my 30 characters (yet to be created).

Depends a lot on what your professions will be and how you want to level them. Power level by buying stuff on the AH or grind the mats to save money.

Some obvious ones to do while leveling, Enchanting (so u can DE), herb/mining, Skinner.

Alchemy/JC/tailoring etc are obvious choices to do later, but then u have to store all the things you get while leveling.

I personally just did Enchanting and saved everything I collected on the way. I got Tailoring on my tank to 325 for northern cloth scavenging when i hit WOTLK content so he could get more cloth as I leveled in instances. Tailoring is far from being a perfect tank profession but I plan to do a bit of heroic farming so will keep it for now since I mainly loot from him.

I plan to power level alchemy/jc on various toons after I've made enough gold from running Heroics. Leveling things takes a fair bit of time as you level your toons, if you do it later and buy things on the AH when they are cheap you can do it much quicker and potentially earning cash easier than getting the mats yourself.

I'm very new to this so others probably have better ideas since they have done it, my first team is a few levels off 80 so will have to see how it pans out. Will be interested to see others thoughts and experience.

I also can't decide what professions are a must have per each team.

I figure..
I need

1 Enchant, 1 Skinning, 1 Herb and 1 Miner.
But thats it?

This is the way I would prioritize, ( I don't mean gathering professions are not useful, just they don't have to be on your main team):
Lowest priority: skinning and herbalism, can be skilled to 350 in one day at no cost.
Next: mining, harder to skill, but still at no cost.
Next: fishing, yes, mats for alchemy, cooking and dailies, ranks above normal gathering professions
Next: engineering, hard to skill, expensive, requires mats from all gathering professions. I love engineering on my paladin tank for pulling, but I treat it as a gathering profession
Next: blacksmithing, not really that useful, unless you have many plate wearers
Next: leatherworking, depends how many wear leather or mail, can produce spell power and attack power gear
Nice to have: inscription, glyphs are expensive but easy and cheap to learn (at least the discoverable ones)
Nice to have: alchemy, create your own potions, transmute is nice, but I get most of my gems from the pvp vendor lately
Nice to have: jewelcrafting, create rings, necklaces and gems at no extra cost
Important: tailoring, create your own cloth armor, most classes wear cloth, all classes can wear cloth
Very important: enchanting, period.

Keep in mind: mats of the current expansion are cheap compared to mats found in vanilla or previous expansions. Craft-able gear is worth less later in an expansion than at the beginning. Mats will almost always be more expansive than the finished product.

Further consider: where do recipes drop? If, like in WotLk, jewelcrafting recipes drop in instances, your main team that does instances should include a jewelcrafter. This pretty much dictates what professions are in what team.

When to skill professions: as late as possible. The greater the reputation, the cheaper to buy skills (I guess, I have never actually compared chars with different reputations). The higher the char's level, the easier to farm mats and recipes.

no professions are NECESSARY, but it is up to you.

it's nice to have enchanting, jewelcrafting and inscription.

The crafting professions like tailoring/blacksmith/leatherworking are ok but most times you won't be wearing crafted gear (only early on in an expansion and then late from raids).

Decide what you want to do.. it is up to YOU.

Either spend time gathering mats now while you level up or expect to pay for them on the auction house. When cataclysm hits all mats will skyrocket in price because of demand. I'd just make sure you have as much done then as you want because it'll cost an arm and a leg to level at that point if you don't do your own farming.

Ultimately you need to find out what you want to do.... do you loot all the mobs now? Do you save the cloth / white items / crafting materials? Would you rather just get to 80 as quickly as possible and worry about it later? We can't answer those things for you.

Herb and mining will fall behind RAF leveling. Since time is limited, i never raised them very far.

I always have skinning and disenchanting on all my teams. Skinning is easy, good gold. But can slow dungeon runs. Like Occulus, I skin all the whelp and dragonkins in the first section.

Disenchanting is expensive. Even with all the drops and quest items, i still have to buy a lot mats to level. Unless you do tons of runs. But in the end, i have tons of dust from heroic runs.

The reason i was always reluctant to do crafting was because armor drops can be better or equal to crafted items. Although there are profession only perks. the only time i bough any crafted items and mats was to start heroics.