Wheelz is right. You didn't say if it was a CS or ST (hard to tell anymore, we've got so many ST owners in here)
Full smokers tend to cook evenly. Guess it's a heat sink sort of thing.
You can use rib racks to get more ribs in. If you put them on all racks, realize some will get done at different times. When I'm doing a full cook, I trim my ribs so they're all pretty much the same size. Or I put ribs of the same size on the same rack so I can watch them.
If you're smoking an already corned brisket, it will probably take longer than the ribs. And the ribs will be dripping on the brisket. Not a bad thing, but might make your beef taste like ribbeef.
Hot spots. You didn't say which smoker. So I'm assuming CS/ST. I temp map my smoker so I know where the hot spots are. The bottom rack closest to the heat will be hotter. The top will be hot because heat rises. With a full load there is less variance, but there is some.
Questions?