Visiting Portugal for the first time - any tips?

Hi all!
Me my partner and our 2 kids (9 and 12 years old) will be visiting Portugal from the 29th of April to the 6th of May. We have only booked flight tickets to fly in to Faro and fly out from Porto.
The idea is to rent a car and cross the country, then fly out of Porto while crossing the country.
We would like to spend at least one day surfing, thinking of the area around Ericeira, as we re all beginners, have surfed mainly in mediterranean and north sea.
Also we prefer more low key, traditional towns and villages and nature rather than touristic areas.

I think it would also be nice to see Lisbon.
One idea was to do part of the N2 as I am reading it is a nice route to follow.

But looking for some advice from you lovely people as well, what are places that you would say we shouldn't miss, what to avoid, areas you recommend we should stay over, things to try or anything else that comes to your mind?

Thanks!