[cheebacheeba]

If you're cooking it on friday, you'd definitely be able to store that in something like tupperware under refrigeration for that period without any problems.
Cooking it the night before...I don't see any problems but it may not be as nice.
An alternative would be a partial cook/steam of your potatoes so that if you needed to cook them on the night and wanted to make quicker work of it, they'd be partially done...in this case there would not be a great deal of difference.
But yes, oil in the mix will likely coat and preserve them, while not allowing them to grey up or anything....as well as many spices having preservative quality.
Just treat with care, keep airtight, keep refrigerated/dark.
Some might suggest storing it in your cooking pot or something made of clay/stone, same conditions.