If everything is new its reasonable to have high pressure at idle. I'm running a stock volume pump and I'm at 45 at idle. But yes, you can run that engine all day with 20 psi at idle, but for your engine and mileage I'd use 20-50 especially with summer coming soon.
I was going to ask this same question until I did a Search and found this thread.
My Stang has 106,000 and only a Mac Cold Air intake with Ford Motorcraft oil filter and 10w30 oil. It's usually at 50 but fluctuates from 40-60....40psi lowest on idle and 60 highest when I gas it.
I was starting to think something is wrong but after reading this post it seems everything is running OK.
But my old 89 vert had 184,000 and was at 15psi to 20psi and lower and still ran good. But it needed work. It would never ever go higher than 20psi.