I never played any of these games but since you said you like being a healer and DPS the most, you should go for a ToS, this class can be incredible in terms of DPS while still providing lots of healing. But keep in mind that the ToS does not use AoC’s melee system like many other classes, you should definitely check some classes out and see how you like it (Barbarian or Assassin for pure DPS melee classes for example).
You should join a guild if you want to learn things (especially for the end game stuff where AoC really begins), random people might teach you stuff as well but in a guild it’s probably easier because they do teaching runs for raids, group dungeons and so on. There are also lots of guides here in the forums for many things.
Try to learn the class you play - there are lots of people out there who got character with insane gear but they utilize their character so badly that even some new players outperform them. Learning a class isn’t hard but it might be difficult because many classes in AoC play very different from other MMOs. Healers for example are not heal bots, but at the same time you should not neglect your healing abilities, there are lots of experienced people and guides out there which you can look up to learn everything in this game.
The server Crom is the server with the biggest population, most of these players are from the EU side so you can expect most stuff happening during EU prime times, US prime times have stuff happening too but it’s not as much as during EU times.
That said, most stuff is happening on level 80, before that it’s not so active, you might find the occasional purist group for low level dungeon (it’s for an achievement to do low level dungeon in their level range) but most people nowdays skip the leveling pretty much and rush to level 80.