You don't have to fill it up completely, to the point where no oil is absorbed. Put some gloves on, and your thumb in it. Turn it around. That's how Subaru guys prime their old filters.1. if filter is horizontal or base down vertical you cant.
From where? Unless you are really negligent, no likely. And I didn't think this needed explanation, but okay: make sure there are no machining debris from threading or deburring hanging around the top of the filter and at the center tube entrance. I think it's good that in 2025 we're still debating if we should prime oil filters.2. Cat says no, Its an easy way to get unfiltered debris into your engine.
The the right way to measure it, before it hits resistance. The resistance to flow indicates oil pressure.After the filter, at the front of the engine above the water pump.