Wow. 400 guests for a first wedding is ALOT. Personally, I wouldn't have taken on that challenge as a first wedding. A wedding is one of the most important days in someone's life, and there's a ton of pressure.

I guess my first question is, what is your experience level now? When is the wedding?

I recommend looking at as many books and magazines as possible. The good news is, you still have the engagement shoot and the parties to shoot before the actual wedding, so you can learn their "angles" and how to shoot them.

I do have a mega-list for weddings (not that I've shot any! One wedding was cancelled a week before the event, and turned into a birthday party...) so if you want to PM me, I can send you the list. It's basically every shot you want to get, and it's fin to sit with the bride and have her rank the shots that mean the most to her...

Also, google "wedding contract for photographer" and there are plenty of samples you can tweak for yourself.
 

Eeesh, I would most certainly be overwhelmed. However, try not to let your nerves interfere with your creative abilities. Since it's your first wedding;

Gather as many examples of images you feel you can recreate, in your own way, as possible from other wedding photographers. This is not a creative crime, we all do it. We all have our moments of creative "grandeur" but who doesn't need a tip now or then?

Write down ideas for photos you would like to attempt. Constantly visualize your subjects in possible scenarios you'd like, this will help relieve some of your nerves the day of.

Contact the bride about a possible set time for family photos they'd like to get. This is usually the most disorganized portion of your day, since most family members are askew and not paying attention.

If possible, shoot all your formal bridal party, bride and groom photos pre-ceremony. This will save you stress getting groups together, who are now ready to eat ect ... and aren't in the mood to photograph. When it comes to those two parties .. do what you can when you can, basically take your opportunity when you see it fit. Most brides aren't so organized that they've got everyone on a schedule. Learn to direct, especially if you're quite as I am.

As for indoor shots, your spot meter, and possibly an extended flash if necessary. You probably shoot digital, if so make sure if the lighting is florescent or tungsten, this will help you know what types of filters to use.

OOoo and try not to feel to overwhelmed by the amount of guests you may have to deal with. When shooting guests in particular, stick to those that really stick out, such as children and old people doing funny or cute things. And don't worry to much about them in general, those are the photos that the bride will frame on her wall. Try to stay specifically with the party, the bride/groom and their immediate families.
 

Since both the ceremony and reception places are indoors, I'd suggest that you go see how they are going to light up the place and practice a few shots, since this is your first time for weddings.
For my first wedding, I took my brother with me so he could help me carry my necessary things around for first taste of a wedding. You seem to have alot of guests, it can be overwhelming, so to have an assistant would be awesome for a firstimer.
Just bring an extra camera, incase. Extra batteries, extra memory cards... Study a list of which wedding shots you should get. In my experience, I study them because when its the actual day, you'll be too busy capturing all these moments. You don't have time to look at the list and check them off one by one. Some do that, some don't... up to you.

Good luck.
 

Don't know if you shot the wedding already or not. I shoot weddings professionally. This sounds like a huge undertaking for a first wedding. One thing I would suggest, is to second shoot or assist a photographer in your area that shoots a lot of weddings, that you admire and respect, so you can see how they interact with their clients. Second, I would have at least one more person shooting with you if not two. There's a lot going on and things move quickly. Fast lenses are a must. If your lenses are sliding apertures, you may have a hard time in the indoor locations. I only use lenses with fixed apertures of 2.8 or larger. Also, noise can be a factor, so watch your iso. Carry at least two bodies, I try and carry three, all with different lenses. You can use flash, but learn how to do "foofing" a great technique by Dennis Reggie (google this technique). You also need to decide the style that your going to be shooting. PJ (photo journalistic, traditional, combo. etc.). Has the client seen your work and are you both on the same page. This is just the tip of the iceberg, but I hope this can shed some light for you. Good Luck.