Even though, in your own mind, this whole thing seems like a disaster, you are only looking at it through @JLeslie colored glasses. I think if I had been a guest at your party (from how you have described it) it sounds like a roaring success.
If you are truly worried about your friend who likes to cook, give her a call and tell only her that you think the party was a disaster and that you had no idea that people would be showing up out of the blue with other food items. Even though this really isn’t true (it wasn’t a disaster at all), you could tell this gal this story, so she won’t feel resentful and she might offer you some sympathy and let you know that your party was really great.
If you decide to have another party in the future decide ahead of time that you aren’t going to stress out and just let it flow how it’s going to flow. If people want to bring stuff, let them. Have one friend or relative (or more, if they’re willing) to be your helpers. That way, when you are in the kitchen frantically finishing up the hot food, your helpers will be shooing people out of the kitchen and telling them, @JLeslie says to go ahead and start on the salad and the appetizers while she’s finishing up the main course in the kitchen, she says not to wait for her, just go ahead and enjoy and she’ll be out shortly. This particular friend will be your gate-keeper and the person who’s job it is to make sure that your guests are doing what you want them to do (without them knowing that that is what you are doing). The gatekeeper is also the person who gets your guests to start by saying something like, “Ok everybody, help yourself to salad and appetizers, we’ve got the salad and the plates over here and napkins are over here. Who’s going to go first? How about you George, come on over here and start loading up your plate” The gatekeeper will also pick up plates of appetizers and walk around the room urging people to take one and removing the empty plates and refilling them with fresh appetizers if you have more in the kitchen (that way you don’t have to put every single piece onto the platter at once, if you don’t want to). The gate keeper will also be in charge of making sure that everyone has a clean plate, cultlery, napkins drinks etc. (So that you don’t have to worry about that aspect of the party). I got this idea from my cousin, who always acts as the gatekeeper at her mom’s parties and it’s really helpful to the chef.
Another gatekeeper is the person, who ahead of time, tracks down extra chairs (and tables if you need them) by borrowing them from the neighbors or whomever. Your best bet is to plan to have about 10 extra folding chairs stashed in the garage so your gatekeeper can grab them when needed. The gatekeeper should also attempt to get your chairs into your garage about a week ahead of time (just in case the lender craps out on you and you have to track down more). The gatekeeper and you can also arrange to borrow extra dishes from whomever is willing to lend some (even if they don’t match) so that you will always have enough, because stray guests always turn up, even if they’re not specifically invited (and that’s OK, nothing to worry about). This gatekeeper should also be in charge of keeping the music going on your stereo (another thing for you not to have to worry about) And this person should also be in charge of disposing of the contents of people’s plates when they’re finished eating and removing and emptying the drink glasses and making sure people have fresh clean plates if they want more (people set their plates down, and they forget who’s was who’s, so you need to make sure you’ve got enough dishes for everyone to get 2 clean plates, even though not everyone will need 2 clean plates and enough glasses for multiple drinks for the same reason and extra cultery and extra napkins) Your best bet is to get 2 or 3 large trashcans with trashbags and place them in your garage or out of sight in your back yard if it isn’t storming, and make sure to have extra trash bags. And if you are having some drinks in bottles or cans, have a big recycling bin too. Peope tend to get nervous if they don’t know where to dispose of their finsished plates (the gatekeeper should ask and then take the plate, so no one has to go into your garage and see the mess).
Then you should have another gatekeeper (it could be your husband, but have a little talk with him today and let him know that next time you need him to remain with you). If you have a helper in the kitchen who is just on standby for anything that you might need, from moving the food out to the dining room, to helping you prepare some of the dishes, to keeping people out of the kitchen, to wiping up spills and removing the trash as you are creating it (shells from the shrimp, packaging, empty cans etc) and handing you utensils and hot pads like a nurse would do for a doctor.
Find your gatekeepers 2 weeks ahead of time. Make sure you have at least 2 and a backup that are willing to commit (if one drops out, you still have another). Let them know exactly what you would like them to do (don’t let them try to figure it out, or they won’t be helpful at all).
Whatever amount of food you are planning to prepare for the “known” number of guests, expand it by 10% to make up for piggy eaters, unexpected guests, or food that somehow gets dropped or burned or whatever (or the dog takes a big bite, yes it has happened). Even if you end up with leftovers, that’s OK. One of your gatekeepers should also be in charge of loading up all of the leftovers into appropriate tupperware to put into the fridge, before it sits out too long. You don’t want to wait until long after your guests have finally dwindled out of your party to start putting things into the fridge. The gate keeper can do this (instead of you) so it’s more discreet and doesn’t make your guests feel like you are kicking them out. You are just preventing food poisoning.
The only reason that I know all of these handy hints is that I used to organize all sorts of huge potluck parties at work, where folks from other nearby businesses would often drop by too. Everything and anything that can go wrong, has gone wrong, so I learned by my own mistakes, how to have everything work out a little more smoothly. Also, I listen to this wonderful cooking host Melinda Lee on the radio every weekend and she used to be a caterer, so I took a lot of hints from her. She is always advising timid folks who are trying to throw a brunch or a baby shower and she’s the one who came up with the idea of the gatekeeper. What a great concept!
Anyway, it sounds like your party was truly wonderful, and I hope that you can look back upon it with fondness too, and that you won’t be dissuaded from trying it again. : )