1. I don't ever mop or baste when I smoke pork butts. That does not mean that you can't if you want to. With a full load of butts, there will be plenty of moisture in the smoker in my opinion. It should not increase the cook time too much if you do want to mop/baste depending on how long you keep the smoker open.
2. I do rotate the top and the bottom racks about halfway through the smoke.
3. I start at 180 for the first four hours for a little extra smoke and then bump it to 235 for the remainder. Depending on the size of the butts, I usually see some coming off around 11-12 hours. The rest will come off over the next 2-3 hours.
Hope this helps. Enjoy! And take some pictures to post here of your cook.