1. Yes. The both the game and the engine are currently in development. Classes, items, quests, dungeons and game mechanics are changed and added constantly between the betas.
Regarding the tilesets: They were still incomplete and thus added if availible. I don't know if they're complete now but I dont think so. In addition the "Online Profile" was added with the current beta.
2. Humm. Depends a bit on your playstyle... As a rule of thumb the ranged classes are usually a bit stronger (at least in the early game) because you can avoid taking dmg very easily if being careful. But the melee classes go well too.
As a race the Dunedain (melee) or Elf (ranged) are strong because of their race abilities.
I'll recommend that you simply think what you'll like to play and then try the class and look at the set of skills if it siuts what you think is fun.
Most of the general tips were already covered by madmonk, so just try it.
In addition, don't forget that the choice of classes/races is quite limited at the beginning. More birth options are unlocked by achieving things by playing.
