Yes getting stamps is no problem as many of the bars, accommodation etc have their business stamps and are used to seeing pilgrims. But make sure you are following Luis's route and you have lots of options for stamps in Albergues etc in the towns at the end of each stage.
On bike it's along the boardwalks (be careful if they are wet, I fell of lightly 3 times in one morning !),cycle lanes, asphalt country lanes or some off road tracks through woodland (mainly dry but with a few wet/muddy patches). A very pleasant experience by bike with not too much traffic except when going through the small towns on route if you keep to Luis's route. Obviously going through Vigo is more urban and from Redondela the roads get busier. But other road users are generally polite and accident rates are low as drivers are used to cyclists here alot. Luis's maps are in spanish but as you say a map is a map, the names don't change !!