Hi Doc, congratulations on your new smoker, and BTW, how did your butt turn out. Hmmmm that don't sound exactly right but you know what I mean.
I been readin' this here forum since back in year 2001 and you'll find two evenly divided camps on laid flat versus hangin' ribs. Personally I think either way will work equally well. The main reason I've heard for hangin' them is so as to get whole slabs out of the smoker and to get more slabs into the cooker. I just lay 'em flat.
Yes, I'd check 'em after three hours but mainly to see how close to done they are. Look for the meat pullin' away from the bones. Bend one and see if it wants to crack in the middle. Poke a toothpick through one and see how easily it slides through. Myself, I like to use the toothpick poke method. That idea compliments to our own Mr. Tom.
Spritz if you want but in a Cookshack it couldn't possibly make them any more tender or juicy. If you think it will enhance the flavor then go for it. Personally I don't do it. Just lazy I guess.
After all that, my suggestion would be to do the following:
Remove the membrane.
Apply the rub.
Cut 'em and put 'em on racks.
Cook at 225 for 3 hours then toothpick to determine how much longer to cook 'em if any at all.
Take 'em out when done.
Foil for at least 30 minutes to allow the juices to redistribute.
Eat and enjoy the fruits of your endeavor.
Just don't make work out of this, it's just too darned easy to get great product out of a Cookshack.
Now go and have fun with your new toy.
