If you do prime don't use regular house paint primer.
Most of the paint that has ever been applied to concrete was without benefit of primer and I personally don't regard primer as vital to a decent porch and stoop paint job in typical conditions
There are specialized concrete primers sold and if you are going to go to the trouble of priming those are the ones to use.
Beware wandering into a maximalist blizzard of rather expensive products; pre-cleaners, cleaners, post-cleaners, pre-sealers , sealers, fiillers, smoothers, primers, base coats, finish coats, post-sealers, waxes, shiners, de-glossers, re-glossers and on and on. It's just a porch.