For loin, I like it done hot. So I'd do it in the WSM, at around 300+ the whole time until it is barely (I mean barely) done. Do it over cherry... it will impart a nice color to the pork.
7 pounds is a lot. Unless you are feeding a large group, I'd recommend halving it and freezing some for future use. But your call on that...
there are lots and lots of interesting things you can do for the pork itself, in terms of rubs, marinades, glazes, etc. Find one you like and go with it. They all work in the smoker.
Good luck and enjoy!