Congratulations!
I got married three and a half months ago so this is all pretty fresh for me. We registered at Marshall Field's (Macy's now), Crate and Barrel, and Linens 'n Things. Looking back I don't think that LnT was a necessity however her family is Canadian and it was the only store that would allow us to have registry items in both countries. We made sure to register for things that were sufficiently different both in function and in price. In our case we received more money than gifts.
As other people said, make sure that you sit back and enjoy your wedding day as it'll be over before you know it. I got the butterflies that morning and couldn't sleep past about 7am. I ended up just wandering around for a bit, took my car in to get it worked on, filled it with gas, washed it, and then started getting ready. That whole morning is a bit of a blur for me. Other than the pictures (be patient, they're worth it), I can't believe how quickly that day went by. Be sure to take it easy during this time, things will most likely go wrong but there's absolutely nothing you can do about it at that point.
You and your fiancee will need to make sure that you have some time to yourselves prior to the wedding. My wife and I made sure that we drove to the rehearsal and rehearsal dinner together so that we could have a bit of time together without other people around. With all of the family that will most likely be around, you'll want to make sure that you spend some time together.
You definitely do not want to miss out on a bachelor party. My brother was my best man and he did an awesome job planning my bachelor party. I made it quite clear that I didn't want anything crazy which worked fine for him. We ended up going canoeing during the afternoon (my groomsmen, a few of my better friends, and me) and then went back to my parent's house and played poker. My friends are scattered all over the country (Washington, Georgia, Florida, and I'm in Michigan) so this was a great chance for me to spend some time with them again. We had the bachelor party on Thursday although the weekend prior will work just as well.
Another thing to think about is the honeymoon. My wife and I went to an all-inclusive resort in Bermuda which was awesome (in case you were wondering). One of the more intelligent things we did was delay the honeymoon until the Tuesday following the wedding. This allowed us time to open all of our gifts, get them moved down to our apartment, and start to get settled in together. I personally think that this is crucial. This also enabled us to spend more time with guests as both of our families scheduled brunches the Sunday after the wedding (we're from the same town). I guarantee you that there will be some guests that you neglect at your wedding so this will give you some time to make up for that.
I struggled with finding gifts for my groomsmen. I wanted to get them all the same thing but at the same time get something that was meaningful and useful to them. This proved basically impossible as they're all very different (engineer, lawyer, psychology major) so I ended up getting them engraved pocket knives. This was a little more cliche' than I would have preferred but it worked. I also included a card thanking them for being part of my wedding. My wife got her bridesmaids makeup bags that were monogrammed and also included a card.
I'm afraid that I can't help you with your final question. In my opinion most tuxes are the same so I don't really see much of an issue there. Your fiancee should obviously look around and find a dress that she loves.
I hope this was helpful. I ended up typing for a little longer than I intended. I guess the single most important thing you can do on your wedding day is to have fun. Even if something does go wrong, there's a very good chance no one will ever know except you and your wife. Once again, congratulations.