Hola
@Kittie_Drente,
I am traveling right now and don't have access to a computer so trying to answer your questions by using a mobile phone.
When I walked the coastal Portuguese in May I did not really know anything about it in beforehand. I used google maps screen shots on my iPad and walked day by day from village to village. I did not have knowledge of any guide book.
Now afterward I know that the first two days I walked on the Senda Littoral which is not way marked very well but you follow the coast line and walk on board walks mostly close to the Atlantic Ocean.
Later I followed the yellow arrows which take you away from the ocean a bit but you can still see it and feel it a couple of kms away to the left. This is what is called the coastal route and you are walking through agricultural areas on cobble stone smaller country roads, narrow paths sometimes through villages and wood more up and down the hills than you can imagine.
So I was mixing the Littoral and The Coastal route without really knowing it.
I never got lost - I always knew where I was thanks to the google maps.
There are not so many albergues on the coastal route as on the Central Portugues or the Frances. I could not make reservation in the albergues I stayed at and most of the times there were I and two other Pilgs i met on the route overnighting in the albergues at nights. This was the two first weeks in May.
The albergues are rare and you maybe have to walk longer than you thought the reach an albergues for the night. You can always book a room - about €30 -40 in May. It is possible to walk from albergue to albergue - but you maybe have to some long distance or taxi back and forth you route a bit (I don't taxi - if I do I have return and walk to taxied parts of the route later). Whatever - you do it your way...
September still being a holiday season in Portugal there are more tourists and maybe some pilgrims en route. I met only two other pilgrims so it was a lonely route in May for me.
It is quite common that pilgrims/ hikers take a train/ bus from Porto up along the coast and start walking from for instance from Vila do Conde or Lavra. Also common that walkers walk back to the central route after one or two days on the coastal. It is your choice but there is no need to do so.
I liked the Coastal a lot and will return in September.
Bom Caminho