I agree with cutting it in half or possibly even thirds due to the size. I cook my rib roasts at 275-300 until I hit an internal of 118*. I take it off, let it sit for 20-30 minutes while I am running the kitchen oven up to 550. I then put the roast in the kitchen oven for five minutes to sear off the outside.
The roast will end up with an internal of 125-130 and be medium on the outside to rare in the middle. If you are looking more for medium, take the internal to 125 before pulling off the FE.
On the pellets, I use hickory. Fruitwoods would be too mild a smoke for me. And at the higher temp, it is running pretty clean anyways on smoke.
Rack, second one up. And since you will two pieces, I would spin the rack 180* halfway through the cook. Say after about 1 1/2 hours. At 275-300, it should take about 18-20 minutes per lb. of the roast. So in half, 10lbs. times 18-20 minutes would take about 3 to 3 1/4 hours.
Keep in mind the extra time to sit and then get seared off for your total time.
Hope this helps.