Although far from the funnest and most creative part of the wedding planning, the guest list is really the first concrete thing that needs to be sketched out. I'm not going to lie to you though, this will be the thorn in your butt until the day of the wedding... then it will be the thank you cards, but that's another post. At this stage in the game, it doesn't have to be a complete list by any means, but a wedding with 30 guests and a wedding with 300 guests is going to be two completely different events!
If you are looking to stick to a strict budget, then smaller is always better. This goes for both the guest list and the wedding party. I don't mean hurt people's feelings, but keep in mind that smaller means more intimate which translates into you being able to talk to all your guests without feeling like the hostess of a NYC philanthropic gala. Additionally, a smaller guest list can be accomodated by a smaller facility, fewer tables and other rentals, less food, drinks, favors, etc. Sit down with your betrothed and start sketching out a list of those people who absolutely HAVE to be there and those you'd LIKE to have there. Additionally, get the same type of list from any parents involved as well. This will give you a great jump on things.
Sometimes having a small guest list is just not possible. It is possible to have a budget wedding with a large guest list, but it takes a little more creativity. If you can't go smaller with the guest list, then go smaller with other thing. For instance, have a dessert or brunch reception instead of a dinner reception. The wedding industry considers this to be perfectly acceptable as long as you plan it for an appropriate time and give everyone a heads up on the invitations. So, don't plan a dessert reception for 5pm when most people are going to be hungry from lunch, but not yet had dinner. Instead, plan it for 8pm and make a note on the invitation that there will be a dessert reception following the ceremony (or something to that effect). That way people can grab their own dinner before they get to the wedding and aren't surprised when they get there. None of these specific decisions have to be made right now, but just be mindful that with a budget wedding, something has to be smaller, either the guest list or the party.
When determining who to send out invites to, think about a few things: First of all, "do I anticipate this person to be in my life at my 25 year anniversary?" If the answer is no, then consider dropping them from the invite list. When it comes to co-workers the generally accepted rules says that if you hang out with them outside of work, then invite them. If you don't hang out with them outside of work, then don't feel obligated to invite them. Obviously, don't hand out invitations at work if you aren't inviting everyone though!
The MOMENT you start collecting names, figure out how you want to organize your guest list, whether it's in a computerized addressbook, an excel spreadsheet, or using theknot.com's guestlist organizer. Keeping this list organized so you know what info you have, and what info you need, will be one of your biggest frustrations. The more organized you can be at the beginning, the better it will be for you!
Next up: The Facility!