Its important if using the 3 2 1 method to establish the type of ribs. Unless you are cooking spares, its summer, its hot, with St.Louis or BB I would highly recommend you back off to at least 2 2 1, or maybe even 2 1 1 with baby backs. I agree with Rodriguez about IT, ribs are a touchy feely kind of meal. The rib bones will tell you. Watch the pull back and I will twist one every once in a while, if it will break out, you are done. I usually do ribs at 220 degrees when smoking at 275 when grilling.
I have marinaded but with the striation of the ribs meat I only saw where a long marinade would effect the ribs. But smoking is about personal preference. I usually rub down my ribs the night before, wrap in plastic wrap and leave in the fridge till I am ready to start the smoker the next day. I am a minimalist, I just like salt, pepper, garlic, and some paprika for color. Although there are some excellent rub recipes on the board. Just use the search engine.
You can add those other flavors during the foiling process, unless you go with the non-foil method. I use some apple cider, apple vinegar, a little maple syrup, and maybe some more rub. But not usually.
If you want to add BBQ sauce, its the last hour, when you are opened up and drying out the steam. The ribs are really already done, but you just like that BBQ taste a couple of coats and its happy happy. That's where to add your sweet sugars, they can and do usually burn on a smoke. So best to stick them in the sauce or use during the last hour.
I think that's your questions, Its fine to marinate, dry and rub. I think the ribs like that over night penetration. Temp is nice but you are dealing with more sheathing material and bone than meat watch the bones or the bend back. Don't foil too long, seriously 1 to 1.5 hours probably. remember you can make it back up in the last hour if needed. Sugars the last hour is its your preference.
Folks are always happy to help here. Good luck with your smoke.
BTW thank you for your service as an EMT.