No Camino experience but small-town Portugal Pascoa (Easter) experience--I would guess that Tomar and Coimbra shouldn't be a problem because they're large and more secular, and Saturday in Rabacal isn't a holiday--but Good Friday in Alvaiazere
might be since Good Friday Mass is likely to be a fairly important town activity, plus Good Friday is a Portuguese statutory holiday and that likely means the front- and back-of-restaurant staff will get paid time off. So the owners may just decide to close, particularly if they think there isn't going to be much business.
Holidays today, tomorrow, and upcoming holidays in Portugal, including types like federal, national, statutory, and public holidays.
If you have access to, and use, Facebook--most of the small Portuguese businesses use Facebook as their primary way of advertising. So in advance, you could use GoogleMaps to locate restaurants/cafes/shops in Alvaiazere, and then Facebook to try and find out details about whether they'll be open or not on Good Friday. For example, you could check out Quintinha, Dutchy's Snack-Bar, O Bras, and probably more if you enlarged the Google map more:
Wherever you stay is likely to have some hints for you, I'd hope.
Bom caminho!
P.S. I see, and had forgotten, that April 25 is also a national holiday--Liberty Day. This marks the 1974 day when the Salazar dictatorship was overthrown in the Carnation Revolution. It is a really fun day--everyone celebrates--but things are likely to be closed then, as well, if you're still on the caminho.
P.P.S. Watch out--whoever wrote this Wikipedia entry was
really into modern Portuguese history and politics--this is a
long Wikipedia entry!