Couple of questions for you.
First, how do you cook your briskets ? Do you cook by time/formula ? Or do you cook by look/feel ?
Second, do you have much experience cooking briskets with the smoker that will do 10 at once ?
Third, on this smoker, have you cooked on all parts of it ? I.e. if the grate is 2 ft x 6 ft, have you cooked on every part of the grate ? Or just a certain area.
Here's why I'm asking these questions. Going from 2 to 10 briskets, things will of course be different. Times will change, the work load will increase, and other variables will change as well. IF you cook by formula/time, it will be more difficult. However, if you cook by look/feel, while things will be different, the changes will be pretty easy to handle.
WRT the "second" and "third", if you have experience cooking briskets on this smoker, AND, you have smoked on all parts of this smoker, that makes things easier as well.
Perhaps a personal example might help. I have a nice sized vertical smoker that can cook 10 butts at a time. I usually only do 2 or 4. When doing those, I usually use the top two racks. I then ramped up to 10 butts for a party. My cook times changed a bit due to more thermal mass in the smoker. Also, my "hotspots" moved, also due to the increase in thermal mass. Those 6 extra butts acted as a heat baffle. When only cooking on the top 2 racks, the lower rack was pretty hot due to it being immediately above the heat. The top rack was also pretty hot as that's where the heat collects.
When I had butts on all 5 racks, the 2nd from the top wasn't a hotspot any longer. The butts there took longer to cook. I also had issues with heat going up the left and right sides of the smoker making those areas hotter, while the center was a bit cooler.
Thing is, none of those changes were a problem as they were all easy to deal with. WRT the center being cooler than the sides, I turned/spun all 10 butts during the smoke. The temp difference between the shelves wasn't a problem either as I just pulled the butts when they were ready. While 10 butts went in at the same time, 4 of them came out first, followed later by another 2, then finally the last 4 came off when they were done.
Again, it was more work overall to be sure, but nothing earth shattering or all that difficult. While my overall cook time did increase, it's not like the time doubled or anything like that. Think I might have added an extra hour or so with opening the door multiple times and having it open while I rotated or removed butts.
As for being sure that the briskets are done on time, there's a number of ways to ensure that. First, Briskets can be held for hours if wrapped in foil or butcher paper and placed in a cooler. Alternatively, you could cook the briskets the day before and reheat them using any of a number of techniques.
This last part might come into play if you decide that doing 10 briskets at once is too daunting task. You could always just do 5 briskets 2 days before, another 5 briskets the day before, and then reheat all 10 of them the day of.