how much is too much?

Go ahead. You'll be fine. I do 4 on a regular basis in my 008, and have done as many as six. Just make sure the air holes are clear.

You shouldn't see much of an increase in cook time. Just make sure you have a pan that will hold the extra drippings or you'll have a mess in the morning.

Welcome to the forum.

Capacity is a relative issue, the smoker doesn't know how much is in there. If you fill it, go for it. There's no absolute answer, but if the capacity of the smoker handles it, why wouldn't it do it?

The two things to remember.

1. Airflow. Keep it open around the food so smoke and air can flow freely

2. Heat, direct vs indirect. The food on the bottom shelf will get a lot of direct heat so it will cook faster. Butts or briskets on this shelf put them fat side down (as a barrier to the heat).

I think you're overthinking it, we see people ask all the questions and try to understand everything before they do it.

As Nike says... just do it.

Here's the key, we'll help figure it out. The only issue will be evenness of cooking is where they are loaded. Just keep an eye on the temps of all of them in case some are ready before others.

That's what using and learning your smoker is about. Just cook on it, experiment on it and it will all work out.

The 25 has three shelves, load two in the middle and two on the top. Put the largest ones on the top shelf. (heat rises, so the top shelf is hotter)

As everyone else says, as long as it fits and there is room for the smoke to get around, you should be fine. I haven't done 4 at once, but I did do 2 8lbers and a 15lb brisket at the same time for 4th of July and everything came out fine.

As Todd said, make sure you have an extra large pan for the drippings, there's going to be a LOT. I filled up an empty 1.75 liquor bottle with all the grease.