We used to do them in the shell without soaking, as best I recall about 350 for maybe 30 minutes or so, so I'd go a bit less than that. If you soak them, that's usually to let a seasoning element, like salt, work its way in; I don't think it'd work so very well to soak them already shelled.

I do not think you have to soak them. I heard that if the peanut is still on the shell then you can soak them, but since you peanuts are out of the shell they would probably just break down and get mealy (unless that is what you want). I would assume just sliding them on a sheet pan and roasting them in a hot oven for a few minutes will be fine.