Cold weather to the north, but there you’ll have the way to serra da estrela (where you may find some snow now) and also beautiful Gerês (amazing landscapes and water springs). If you drive to the south it Will be warmer and you’ll find beautiful wild beaches and much more (go south through the sea coast). I guess you never find too much people traveling through Portugal during the winter and outside of big cities. Lisbon has many tourists all year. Porto too. But the rest of the country will be quiet i think.
About local food, i’m not the best one to suggest since i’m a vegan and portuguese food is all about meat and fish. But we have the famous bacalhau (cold fish)! Bacalhau com natas, bacalhau espiritual, bacalhau à Brás… Many different dishes with bacalhau. With meat, ‘cozido à portuguesa’ is our most famous dish. But you won’t find it hard to find traditional restaurants!