My house is 30 plus years, I have a slate stone
floor in my foyer that needs cleaning and then
sealed. What do you use for this project??

Try a good stone cleaner made by a reputable company like AquaMix, Miracle, or Stone tech Pro. There are some other good ones out there but I forgot their names. You could also get some from www.mbstone.com
AquaMix makes a very good sealer called Sealers Choice Gold.