Congrats on your purchase.
You didn't mention the weight of the B-backs. Assuming they're in the 2.5 - 2.75 weight range, using a temp of 250, they'll take roughly 3.5 hrs. I have little experience with smoked stuffed Jalepenos but I'd guess 1.5 - 2 hrs would be sufficient. A more experienced pepper smoker might advise more or less time.
Start the ribs first. I'd also suggest placing the peppers under the ribs to avoid cheese filling dripping on your ribs. If you haven't already done so, read thru Smokinokie's "Ribs 101" found
HEREIf you're new to smoking, you can test rib doneness with a toothpick. At the 3 hr mark, insert a toothpick between the meat & bone, top thru bottom. When it slides thru with ease, they're done.
Some cooks prefer to smoke ribs at 275. Start with 250...it's a good middle ground. Keep notes of all your smokes. You can adjust temps to your liking.
Good luck. Report back with the results or any other questions.