Welcome to Just Answer and thanks for your question. Either temperature will get the pork cooked, but I like to cook mine on low since slow cooking makes pork more tender. It is mostly a matter or preference.
Yes, it will cook all the way through in 7 hours. Just leave the lid on it the whole time. It doesn't cook as well if you peek. For large pieces that I am cooking for barbeque, I have to cut them so they will fit and the lid will go on tightly.