Hi Neve
I am looking at southern Portugal for April 2018. I did Lisbon to Santiago last April.
Temps were fine, little rain. Don't know why folks complain about the walk out of Lisbon, or the flattish walk thru farmland for the first few days. It was fine by me.
I also love the seaside and further north walked it as much as I could.
I need to muddy the Portuguese waters further by advising that I heard several times about a "Seaside Route", not the one mentioned sometimes as adjacent to the "Coastal."
Generally this came from French walkers who had walked a mix of trails up the Rota Vicentina, and were continuing up past Lisbon on this "Seaside Route" via Sintra.
Whatever, here is a website I am investigating re the Rota Vicentina .
http://en.rotavicentina.com/kiosk.html
And a variation of it;
http://en.rotavicentina.com/go.html
As I have plenty of time I'm thinking of rental car/bus/train from Barcelona down the coast to Valencia, then on to see Cordoba, the Alhambra, Gibralta and Cadiz. Just touristing. Then walking Cadiz to Seville on the Via Augusta. 173ks.
Then across the border to walk some variation of the Rota Vicentina.
Whatever, keep your eye out for any mention of that Seaside Route - and let me know if you find anything!
Regards and always good travelling
Gerard