I say go for it!
Cook the Brisket very similar to how you cook your butts. 222-250 degrees. Your slicing the brisket so you dont really need to get up the 195+ like you would to pull a butt apart. I would take it to 190 IT and wrap and rest for an hour. Just like the butt assume 2 hours per pound. Toward the end get a pan and catch drippings from the brisket. If the brisket comes out on the try end use the drippings to mop on like a sauce..you can add some tomato paste or anything else to it if you wanna give t a different flavor.
Also slice across the grain. find there the brisket flat comes to a tip and slice across that. Oh this reminds me of something else...are only smoking a Flat? or the whole packer brisket (point and flat)? For your first time i would just do the Flat if you haven't already bought the meat.
So yes you can smoke the ribs, butt and brisket all together.
Let us know how it comes out! and if you have any other questions post them and i'l check back on this