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.
Over the years Blizzard has been steadily taking the best ideas from the UI customization community and integrating them into the base UI. For example, the game now has a built-in version of QuestHelper which shows (on your map) where to go to kill monsters for quests and turn them in afterward. Frankly, there are no "vital" leveling addons anymore.
Some addons can be useful, of course, but it depends more on your own play style rather than "here's a list of what you need to play the game".
My advice is to just start playing with no UI addons, and wait until you find an itch that needs scratching before you bother installing any.
Best Answer
What you want to aim for is: Focus Fire -> Kill Shot (if available) -> Kill Command -> Arcane Shot -> Cobra Shot.
I would also recommend not going BM for levelling. The Marksman talent tree (along with a few talents from BM) will allow you to DPS non-stop while in dungeons.
Hope that helps.