First of all, hello

.
Well im a hardcore World of Warcraft PVE player, but i got kinda bored recently as i've done basically anything possible in this game already.
I've been waiting to play GW for a long time and now ill probably be finally starting.
Ill be buying Classic, Factions and Nightfall.
I got "two" questions.
1) Is it still worth to start playing at this time? I've read that GW2 is on it's way and that i'd need around a year or so to get to the "acceptable" skill of a player.
2) I play on WoW as a retribution paladin who like to mainly DPS(do damage) and to Tank, so as i've read there's many classes that can tank, right? I tough the warrior of GW would be similar to a paladin in WoW. If not, what class is decent at damage dealing(that a good player can put on more damage than people do on pure damage classes) and good at tanking?
Healing classes is out of question. I don't like making people stay alive by healing em.
1) Yes it is, especially if you want to play something different than the WoW
2) In GW, except for certain team builds and comps, there is usually 2 healers (backliners) and 6 "DPS" in an 8 man group, there are exceptions but that is the general jiist of it.
I would consider looking at the guild wiki and checking out the articles they have for each profession then try out said professions (if you bought Proph Factions and NF then you have 8 character slots) that interest you.
After you get to level 20 (max level) and progress through the game give PvX wiki a visit and check out some of their builds afterward (or just make builds by yourself). Focus on what makes them powerful instead of ctrl+C'ing the builds so you understand what the overall community feels what the top damage dealer / useful build is for that profession.
Do not roll a Paragon as your main character if you like variety in your primary PvE profession, at the moment there is only one build that they truly excel at (and everything else is crap compared to what others can achieve).
You played a Ret paladin in WoW, and probably other classes, when designing your builds try not to overextend your skills, a warrior for example does not need self heals in PvE, they should be focusing on killing stuff (when grouped with others), same with a necromancer, elementalist, assassin, dervish yada yada. In WoW you can use all abilities available to your spec, this is not possible in GW.
Try and join a guild, you won't expect much competent pug activity in a 5 year old Free to Play game since most of the population has already done that content and has learned they can do it faster and just as effectively if they do not waste their time waiting for pugs. If you do not like this, you may not enjoy the game at later levels.