1. Hard to say best healers, all have their good points, might go with Guardian or Water Ele. Both of those do great support.
2. Dungeons are relatives of Sorrows Furnace, but with gooder rewards, there are achievement rewards for doing each path after completing story line of a dungeon.
3. Collectors? Yes that is why you get the tokens specific to each Dungeon.
4. Traits are a means of making a toon better at different skills and functions, with a variety of "skills" available at each trait line level. You cannot max out all trait lines all at once. You wind up specializing in just a few trait lines for an effective toon. Traits can be swapped around, and you can earn or buy trait "skills" at different levels of each trait line. IE a Necro can specialize in Minions, Wells, etc. Match your traits to weapons and skills. PLEASE READ WIKI.
5 Dailies are much good stuff for learning and earning.
6. To start with equipping armour with rewards and finders is usually good enough, once you get to 80 craft 80 lvl exotic or go to Orr temples to buy 80 lvl armour with karma. READ WIKI ON CRAFTING LEVEL 80 ARMOUR. ONLY BUY 80 LEVEL CULTURAL FOR ACHIEVMENT OR SKINS.
7. Hall of Heroes skins, and cool pets. Wonderful Black Widow through HOM