First off, welcome to the family!
A couple things you should consider: I have no idea how accurate the door thermometer is on the smoker, but most need to be calibrated. I would run down to your dept store otr hardware store and grab an oven rack thermometer right away while you can (hope they're not closed for the night already). With the oven rack therm, you can at least have two readings to go by. We can talk calibration later, but get the rack therm ASAP.
Smoke the ribs @ 225*. If you want tender ribs with some bark/crust on them, smoke 3 hours open grate, 2 hours wrapped in foil, then 1 hour back on open grates. We call it the 3-2-1 method for spare ribs. For Baby Backs, go 2-2-1. For really tender, bone-popping ribs, go 4-2-0 for spares, 3-2-0 for BB's.
Come on back when you've seasoned the smoker. Oh, put the oven therm in when you season, then you can get a better idea what's what with the door therm before you start your smoke.
We'll get you through it, no sweat...there's a first time for everything.
Eric