Hello Nici: I cycled the Caminho Portuguese from Lisbon to Santiago in September of last year.. I spent several days in Coimbra which is a beautiful town to explore as it is full of history.
I revisited my journal covering the area between Coimbra and Porto. My journal notes stated that the Caminho markings going out of Coimbra are not very good. Many of the towns outside of Coimbra seemed depopulated. Much of the Caminho follows the highway N1. Mealhada which is between Agueda and Coimbra stands out, but only because the area is known for its roasted pig.
If I were you, I would visit Fatima before going to Coimbra. After Coimbra, I would take the bus or a train to Porto and rejoin the Caminho. The area north of Porto along the Caminho (interior or coastal) is far better marked and enjoyable.
Bom Caminho