First, you don’t want to be putting cold beef in. Let the beef warm up a little before throwing it in the KK. For briskets I’ll take them out of the fridge before going out to start my fire. And I usually do a good 3 hour heat soak before a low and slow.
As far as fitting them you could put two on the main grate and one on the upper grate above them
You don’t really need three probes, I’m not a fan of MEATER, they always disconnect on me. Thermoworks has a new wireless setup that people seem to love. Get a Thermopen One for checking them and move them around as needed. Thermoworks also has a good controller/fan combo that is really popular, Billows. Fireboard is also popular. I did not like my Fireboard pro when I first got it, I was seriously overthinking it by trying to setup Programs, once I just set a temp and alarms I really like it.
if you can’t get cocochar just get the best you can find locally. I’ve been using B&B as it is what I have access to, it is fine. As far as wood the KK coffee wood chunks is great for beef, or Texas Post Oak from FruitaWood.
I don’t know where you read those things about controllers but I’m sorry, that just isn’t the case. That is just my opinion so take it for what it’s worth. I use one on every low and slow. If setup properly they are a great tool that will make your life easier. I’m not as young as I used to be, I like to sleep at night.
Depending on the size of the briskets you are probably looking at a 10 to 13 hour cook. And factor in at least a 4 to 6 hour rest (FTC)
So think about starting the fire around 9 PM, get it stable at 235 degrees, briskets on at midnight. Wrap at 8 or 9 AM and finished between noon and 1 PM. Then into the cooler.
And honestly I would get all of this stuff together asap and throw a couple pork butts in and have a practice cook. Pork butts are really hard to screw up. Briskets are easy to screw up and they are not cheap.
Hope that helps.