DominionStrategy Wiki
You are the brashest scum player on f.ds.
Purchasing The GameDominion is awesome! What expansions should I buy next? - There is a post over on the blog which tries to answer this question, and you can find a few forum threads (1,2) on the subject as well. If you are looking for more information, there are also a few threads (1,2,3,4,5) which compare various attributes of the different expansions.
If you want to save money (assuming you'll eventually end up getting everything), you can start with the big box (includes base/alchemy) and then add another big expansion like seaside or prosperity for $100.
I'm a fan of Intirgue and Prosperity. however, that just seems to lead to playing BM most of the time.
Is seaside easy to play in RL? Are duration cards more annoying than fun or vice versa?
Nah, it's not particularly annoying. You'll forget to keep durations out on occasion, but after a while you'll get into a habit of setting them a little to the side or turning them sideways or something and everything will go smoothly.
I don't like intrigue. Too many cards that change nothing (Secret Chamber, Great Hall, Wishing Well, Coppersmith, Ironworks, Scout)
Mafia play advice: If you are not content with the way the game is going, always assume that it is your fault.