What temperature, in degrees, should I set my slow cooker to for a 5-pound pork shoulder?
I'm pretty sure that no matter what you do, it's going to end up braising, so it doesn't really matter exactly what temperature you set it at.
The manual does have suggestions for this:

Start with 1 1/2 to 3 pounds of beef or pork... [various cuts]
Preheat multi-cooker at 375˚. Brown roast in... [various oils]
Add 2 cups... [liquid]
Turn heat control down until pilot light goes out. Cover and simmer 1 to 3 hours or until tender.

So you can do it like that, and presumably that'll help get things going quickly and maybe get you some nice browning.
But the meat is going to release water and fat, and at that point it's basically like any slow cooker: you'll have liquid in the bottom, and steam held inside by the lid. As long as there's liquid left, it can't really go above 212F/100C.
The suggested 2 cups of additional liquid is presumably to avoid sticking to the bottom and burning; you can probably get away with way less, likely even what the meat releases naturally. But until you figure out exactly what works in that particular cooker, you'll probably want to check in on it after a while, and add more if it seems like it's sticking.
And yes, a braise should have a pork shoulder done within 6-8 hours.