1) Try
this for a free, playable demo of EQ2. It has a very nice tutorial. Remember, it's just the beginning.
2) There are literally thousands of quests to do, but that is not the only was to experience the game. You can group, solo, adventure, roleplay, PvP, and craft.
3) Not much change there, Healers are always popular. However, you could form a group of almost any class makeup to be effective. For hard, epic mobs, you'll want a healer.
4) There really is no best class or race. Different races will have different beginning stats that may lean to a particular class. Erudite has a higher starting INT (good for Mage), and Ogres have a higher starting STR (good for Fighters). However, eventually you will get gear that boosts your stats well beyond that, and will overshadow what slight beginning difference there was.
Races are pretty much equal, no-one has any particlar game-breaking ability. SOE worked hard to make all races equal. So take this opportunity to go outside the box. Troll Paladin, High Elf Necromancer, Halfling Monk, it's all possible!
Classes don't have a best, they just do it differently. Of the healers, Templars have large single-hit heals and wear plate armor, while Wardens have Heal over Time (HoT).
In the Scouts, a Ranger is a master with a bow, while an Assassin has the largest single melee attack.
For Mages, Wizards have the biggest nukes, while Conjurers control elemental minions to do their bidding.
Fighters also have different types, a Guardian has the best defense, while a Monk uses Avoidance to not get hit.
5) There are many UI's to choose from
here. I and others use one called Thor, but you can pick from a large selection.
6) No change here, Mages wear tissue-paper-thin armor and can't take a beating. The Priest line would seem to fit your bill. Shaman's are considered Battle Priests, but the Templar wears plate armor. However, Wardens have many self and party buffs and can do fair damage. Everyone will have a particular preference to a class, especially one they play. :)
Keep in mind, Priests are not a DPS class, and will not do amazing damage. That is reserved for Scouts and especially Mages.
You can try several different classes to see which one you prefer. Good luck!