I cook at 250 and consider temps from there to 275, kind of a middle of the road temp. Not slow and low like at 225 or below, but not hot and fast above when you get above 300. Some do it for sleep, some do it because that is their pits sweet spot.
As far as finishing temp, it's still determined by the probe test, no matter what the IT is. I rarely probe for temps anymore on my briskets, from start to finish, no probe enters 90 % of the ones I cook because I know my timelines at 250 on my pit. I know that after 4 hours of smoke, it's wrap time (which the brisket will typically be in and around the 160 IT mark by this time), then I'll need to start checking for tenderness around the 3 to 3 1/2 hour mark. If my pit has fluctuated more on the high side of 250, then I probably will start checking around 3 hours after wrapping, if I have ran on the low side of 250 (which I will for comps because I like my ribs below 250), then it will probably be closer to the 3 1/2 mark.
As far as removing fat, I do a heavy trim on the meat side surface and take all but a little of the fat of where the flat and point meet whether I'm cooking Select, Choice or Prime, so that really makes no difference. As far as the fat cap, I'll trim the heavy stuff off, but always leave a nice layer on the bottom side. Once cooked, it all just slides off or can be scraped off easily. Depending on your cooker though, you might want to use the fat cap as a heat shield, especially with the high $ meat you are cooking. Other than that, the fat cap does little to nothing to improve the end result of your product.