Welcome to SMF glad you joined us. Congrats on the new smoker.
For all the things you mentioned you can smoke at 225 or so
The Chicken Breasts you might consider wrapping them in bacon. It will keep them moist and everything's better with bacon right Smoke them to an internal of 165 degrees. The skin on poultry usually comes out kind of like rubber and many of us will crisp it on a grill or in an oven, If you weren't doing other stuff I would suggest cranking up the temp in the smoker but that won't work with the other meats.
Baby Backs I would suggest 2-2-1 which basically means put them in the smoker for 2 hours then take them out wrap them in foil add a little liquid seal tight to allow them to braise for 2 hours then unwrap them and stick them back in the smoker for one hour to firm back up. If you want to baste them with sauce do it during the last 30-45 minutes that way the sugar in the sauce doesn't burn.
Tri-Tips I can't get down here but basically add your seasonings think something like a Montreal Steak Seasoning and smoke it to 135 or so then take it out and foil tent it to rest then slice
Don't forget your looking for Thin Blue Smoke (TBS) not billowing white smoke. You should barely be able to see the smoke or not see it at all and just smell it. If you can smell it so can the meat
Good luck with your smoke