Is it true that the raids are progressive, i.e. you have to begin with Naxx to unlock Ulduar etc? How's PVP/Wintergrasp and general economy and "community"?
Yeah, they're like that on Dalaran. Goes like Naxx->Uld->ToC10/25->ICC, with the usual EoEs and VoAs inbetween. Guilds host "carry" raids for their new blood all the time so that they can get more people to smash through the usual loot treadmill of ToC and VoA, but you can generally find people willing to just host a pug Naxx or whatever.
PvP seems fine, although I mostly played some casual battlegrounds (which I didn't generally have a problem with finding and joining to) and ran some WG on a PvE character with 0 resil, so I wouldn't say I'm an expert, but all the inner workings (arena and whatnot) seem to be business as usual, complete with the drama about That One Guy Who Plays Human Sub Rogue And Gets Accused Of Cheating Because Reasons. Generally with WG I sometimes noticed moments where, for instance, Ally would show up for WG defense with only like 10 people and Horde brought like 40, stomping everything. And vice versa. I'm not sure how it's like on other servers.
EDIT: I asked around and more oriented people generally say that Dalaran pop is too low for proper PvP. 2v2 isn't terrible, and that's the best they can admit.
General economy was fine for a while, but then there was an invasion of spambots that sent everyone a fuckton of free gold and it elevated the prices of stuff by quite a bit, and I remember being really annoyed when a stack of Rugged Leather could cost a couple hundred gold. I think it chilled down a bit and it's not unseemly to think that you could level up a whole profession with just being shrewd with gold, I know people who make 10k in like a day once they sort out their crafting profession, and there's always someone who wants to get some money from Enchanting/LW/JC commissions.
"Community" is, eh... well, if you go on Global, be prepared for quite a lot of /pol/talk out of nowhere, the usual "anal [Thunderfury, Blessed Blade of the Windseeker]" jokes and the usual juvenile drivel. It's not generally hard to find a decent guild, and there've been a lot of environments in my experience that would either go on casual, friendly raids or would strive to go superhard at progression (Horde seems to be more "PvE-competitive" of the two sides because IIRC they got realm first heroic Lich King kill). For every unplasant shitter type like that guy who spoke no English and went with a fantastic 0/71/0 Retribution spec (ALL PvE AND PvP talents) into Ulduar and then proceeded to not understand absolutely any Mimiron mechanic and blamed the Holy Paladin for not HoSing him in time while he was running through all the mines, I could generally find a fine bloke.
Raids mostly work fine and the only thing I can think of is that I never properly went through was the "Safety Dance" fight in Naxx (Heigan the Unclean, I believe?) because everyone just stacks on the rock and avoids the acid. Mimiron is bugged in such a way that if you taunt him in 2nd phase, he goes apeshit and instakills everything. ICC went live without the +30% HP buff and Saurfang would eat your limbs without a good Hunter and perfect Blood Beast kiting, but then they tuned ICC down and more people got their Kingmakers. About the only thing that I can think of that most WotLK servers struggle with (both Warmane and Dala) is that pet scaling is bugged and I'm not sure if that was ever fixed, so be aware of that if you wanna roll pure Demo Warlock (Demo/Destro hybrid murders though) or a BM Hunter (though you can still gank people by shadowmelding while the pet instakills wandering clothies).
That's my general experience as someone who mostly raided casually, spent most of his 80 time chatting with guildies in Dalaran unless it's time for a raid, still has to get his Kingmaker and gets quickly bored of one spec.