Returning and Re learning

[Anova]

Since you've already played the game, you have a good idea about how the classes and dungeons work already. And that's accounting for almost a year's worth of absence.

DPS queues can be long, and I suspect they will get much longer once patch 2.4 hits. Currently, most queues for DPS are 20-30 minutes, while tanks are nearly instant. Healers are maybe 10 minutes at most. These times are generalizations and will change depending on what time you log in.
Of the two tanks, Marauder is easier if you are simply leveling up. They get their main tank mechanics faster and it is easier to keep enmity for speedruns using overpower. These overall make smoother dungeon runs, which will be useful if you're grinding them for levels between quests.
Healing you already know, but you're welcome to give arcanist a try. It is very different from WHM and it allows you to pursue both a healer and dps class you can switch between for solo and party play.
As for dps, thaumaturge and archer are probably the easiest to handle.

Either/Or is fine, although I find that healing benefits the most from KB+M more simply because of the versatility of the mouseover macro. It is a personal preference though.

As for servers, Leviathan and Coeurl both seem to be good choices. They're both active servers with lowbie-friendly players. If you choose Levi though, give me a notice. I'll send some starting gear to help you start up.