First time sous vide for a large cookout

I'm going to copy and paste your questions to try to make sure I answer them all:

• Does it matter how much chicken I have in the bag as long as it's one layer?

Yes. A sheet of food has less surface area than individual pieces, so will require a slightly longer cooking time to make sure it gets up to the proper temperature. You also don't want so much food in the bag that it doesn't fit in the container well... you need water on all sides of the food.

• I haven't decided what type of container I'll be using for the bath quite yet. Should I try cook everything at once? In batches? Continuously(one in one out)? I'm searching for a used large cooler currently.

You can use just about anything as a vessel (so long as you can figure out a way to attach the circulator with the proper depth of water), but there are limits to how much heat a given device can put into the water, so a smaller home device might struggle with larger water volumes and large amounts of cold food being added all at once. The advantage to a larger container and a single batch is that you can hold it ready for the grill, without needing to take up lots of space in your fridge cooling down prior batches, but then you also have more work to do on the day of your cookout.

The container needs to be large enough to not only hold the food, but hold the food with water in between each bag. (some people will rig up something above the container with clips or similar to hold the food at an even spacing). And you can add some hot water in the beginning to get your tank up to the proper temperature, rather than rely on the immersion circulator to do all of the work.

An insulated container like a cooler is useful for large and longer batches, but large plastic vessels work well, too (with some sort of a cover to keep it from losing too much heat and water to evaporation), but you can even use a large metal pot in a pinch... but it helps to put it in a cardboard box lined with towels to keep it insulated.

• I'm planning to marinate for ~1 day, then cook in the sous vide bath. How long can I store them in the fridge after that before the cookout day?

It depends what temperature and time you cook them for. If you pasteurize them, you should be able to hold it for longer... but beware of acidic marinades which might continue acting on the meat and turn it to mush.

• How long do I need to ice shock things for, I've done some research and it seems to vary widely. I've seen 10 minutes, 30 minutes, 2 hours? Help.

It depends on how large of an item you're trying to cool down, and how much heat it's holding. The larger and hotter the item, the longer you're going to want to chill it.

• Is there anything I'm missing or overlooking in my plan? Thank so so much!!

I don't think so, but I've never tried to do what you're doing at this scale.

• P.S. One of the books I've been referring to is Sous vide for the home cook by Douglas Baldwin. All the times in that book seem to be quite a bit longer than other resources I've checked. Is there a specific reason? It seems like a great resource otherwise.

I haven't read his book, just his website that has all of the reference tables for cooking and cooling. As well as I'm aware, it's the gold standard for sous vide cooking, as it covers much more detail than many others (considering the shape and thickness of the food, whereas some others just assume that all 1lb steaks are the same same thickness). I've personally had no issues with his times and temperatures, but I also haven't bothered following anyone else's advice since someone linked to his guide on here many years ago.