Usually don't need to seal if painted with oil based paint which is what you should use unless you do the epoxy paint made for countertops.
This may help: https://www.hometalk.com/31363097/spray-paint-glaze-kitchen-counter-make-over
Hi Liz: Here are a couple of sites that should help you out:
https://lifeoflaurenlou.wordpress.com/2013/01/16/finally-the-kitchen-countertop-post/ This one is a fun read :)
And, this may be closing the barn door after the horse is gone, but:
You're welcome. Good luck with your project
Epoxy resin is good or an oil based polyurethane.
Use any polyurethane.
Hope this Helps! Jeremy - https://do-daddy.com