You can look up all the information you need in the Compendium (spelling? -.-) on the POL Viewer. That's actually where you need to go to fill out your application to get married.
Actually, you'll need a chaperone to do that part for you. Someone you know and trust will fill out all the necessary information for you and your request will be put into a marriage "lottery" and if you're lucky, you and your love will have your wedding on the day that you asked for. Yes, it is completely random, as there are undoubtably thousands of marriage requests from all of the servers. I think the GM's actually host these weddings which is why you can't just get married right on the spot.
Tetsume and I have tried for a wedding for a long time, and we've always gotten mail back saying that we weren't selected for marriage. So if you are interested in having a wedding, I hope you have better luck than we did!
Umm... you can have wedding in just about any area you want (as long as it doesn't interfere with anyone's EXP or Quest and is SAFE for all the guests). Of course, there are also a few places inside towns that you can choose as a "default" wedding, these areas are listed in the compendium along with the form you can fill out if you want to be wed elsewhere.
Ahh, the cost of your wedding will vary depending on the area and size of your ceremony. You can choose to have 10, 20, 30 (I don't remember exactly though :P) guests come to your wedding and I think this includes the chaperone, bride, and groom, though I'm not 100% positive! They all get fireworks and stuff to use at your wedding, and make sure they all behave! The GM's won't tolerate misbehavior, I think they would even cancel the wedding if the guests become to rowdy.
Also, you can choose whether or not you want to buy the wedding dress set for the bride. It looks exactly like the Opaline Dress set, but it's level 20 and Rare/Ex. Oh! And both bride and groom must be at least level 20 or higher to marry. Unfortunately, there are no tuxedos that the groom can wear :( so make sure he dresses nicely! Try to get him an Aketon or something ^^
Rings... You can have them engraved with initials or the other partner's name (I think this is the better choice ^^).
That's about all I know, if I'm leaving anything out, it'll definately be in the Compendium.
Hope this helps :P