I have joined this server today and heard a lot of good stuff about it.
Last time i played WoW was about a year ago (maybe less) at the beginning of shadowlands on retail.
My question is: is there any importance to the character i choose? for example i really liked shaman but its very hard to get into dungeons and raids sometimes because its "not needed" or "not meta", so i wonder if it any different here.
Also, for a casual player who wants pvp and raids, is Frostmourne good for me?
Dungeons are always easy to get into. Some PUG raids allow DPS shamans too. But for the true end-game content, shaman has one spec to play, and that's resto. You'll need to earn your spot before people start accepting you as DPS.
Frostmourne is seasonal, with Naxx, VoA, OS and EoE only available from raids at the moment. The content is tuned to be bit harder than regular WotLK. Icecrown is realm where people tend to play, as it's high rates, and very active in PvE and PvP. All content is already unlocked and there are no resets to progress or anything like that. All sorts of players play there. New, old, casual, tryhard, young, old, stupid, smart.. You name it.