Keys to heroic instances in BC are bought from the vendors for various reputations at Honored rep.
- Thrallmar/Honor Hold for the Hellfire instance.
- Cenarion Expedition for the instances in Coilfang Reservoir
- Lower City for the Auchendoun instances
- Sha'tar for Tempest Keep
- Keepers of Time for the Caverns of Time stuff
and for Magister's Terrace you must complete the quest for it in regular difficulty.
For all the rep based ones it's pretty easy to get enough rep just by question, if not doing one or two regular instances.
A list can be found here.
http://www.wowwiki.com/Instance_attunement
In terms of classes, trying to cover all three roles between the two of you is a good target. When you guys are questing together by yourselves, having one person be DPS and the other healing helps keeps downtime to a minimum. And if you guys decide to use the Dungeon Finder, having one person able to heal and the other be able to tank ensures you'll never have to wait long in the queue.
Blizzard has homogenized the classes over the years so there is a tremendous amount of overlap between the classes and specs. As long as you guys cover the three class roles, feel free to choose whatever fancies you.
For reference the hybrid classes are:
- All three roles: Paladins, Druids
- DPS + Healing: Priests, Shamen
- DPS + Tanking: Warriors, Death Knights
If you're going to take my advice about role coverage, you'll want to avoid Mages, Hunters, Warlocks, and Rogues as they can only be one role: DPS.
Since you're talking 1-85 play, Death Knights are off the table as they start at level 55.
Putting it all together:
- Person 1: Paladin, Druid, or Warrior (to cover tanking)
- Person 2: Paladin, Druid, Priest, or Shaman (to cover healing)
In terms of professions, I'd avoid the heavy crafting professions that take a lot of time to level up and are usually taken for the Bind-on-pickup endgame recipes: Blacksmithing, Tailoring, Engineering, Leatherworking. Instead, focus on the professions that'll let you help each other out while leveling, like Enchanting and Alchemy, or the gathering professions, like Mining and Skinning, which will prove lucrative and won't require too much (if any) time soloing.
Best Answer
If you're not min-maxing at the level cap, your best bet will generally be at least one, if not two, of the three Gathering professions, Skinning, Mining, and Herbalism. If you do decide to take a crafting profession, choose the gathering profession that meshes most closely with it (i.e., if you take Leatherworking, grab Skinning, Engineering, grab Mining, or Alchemy or Inscription, take Herbalism.)
If you want to make money using a crafting profession, the best choice before the cap will be Inscription, as the Glyphs you can produce as early as level 5 will be used even by level 80 characters, providing you with a constant market.
If you want to produce things you yourself will use on a regular basis, Engineering provides fun toys, and trinkets at much lower levels than they'll be availiable as drops. Leatherworking allows you to make your own armor, but drops and quest rewards will, for the most part, be better than what you can craft - at least until the Cataclysm expansion releases. Alchemy will allow you to make a variety of useful consumables, but in general, you will have to make many more than you'll be able to use as you level, and there won't be much of a market for what you craft.
Enchanting is a viable option as well, and you'll be able to enchant your own gear as you level, which is handy.
Realistically, until the +Stat bonuses at 400+ skill come into play, there really isn't a 'best' or 'most useful' profession. There are a few that will be much less useful to you as a hunter, such as Blacksmithing and Tailoring, but for the most part, you should be fine picking out whatever you find fun.
The only other major note worth making is that each of the three gathering professions provides a free 'passive' boost as well. Mining will give you some extra Stamina for free, Skinning will give your character increased critical strike chance, and Herbalism will teach you Lifeblood, a free Heal-Over-Time spell you can cast on yourself on a short cooldown. The crit from Skinning especially should be very handy for a low level hunter, though the other two perks are nothing to sneeze at either.