Get ready for a wonderful treat! Especially prime and at that price!
You seem to have a good plan. You could leave a little more fat on the flat, that may help. But, other than that, I’d smoke it whole. I have not cut a brisket in my time smoking. The temps seem to be right and the brisket comes out wonderful!
If anything, you could wrap the brisket once you get the bark where you want it. That may help retain some of the moisture in the flat. But, I haven’t done this method as well - I just let it go until its jiggly good and probe tender.
And your last question, I’d use two probes, one in the flat and the other in the point. Just so you can monitor the temps. They may be 5-10* off for a bit, but by the end, the temps seem to catch up or even out.
Have fun! - oh, what are you going to rub it with? That’s always the stuff I want to know!