Disclaimer: these suggestions are based on my experience and do not have any support from any of the suggested places on this mini guide. 

Another thing that is important is that Porto is terrible in terms of traffic and parking. Please, do not take the car to this city. Use public transportations and you have a direct connection to Porto by Metro in Vila do Conde here.

Here goes my recommendations:

So, to be on Porto you MUST go to the wineries (Port Wine) and one of the best is this but I don't know if it is open at the weekend (please check first):

• Taylor

• Or this one: Grahams

They are more expensive then the regular ones (+-15€pp) but quite best.

If you can't go to one of them, go with the wind and choose one, lol 

At least one visit is mandatory to any winery

You can grab an Hop on Hop off to see the city and please check if there is the package Bus+ 7bridge boat

Places you must go walking:

• Torre dos Clérigos and the surroundings

• Livraria Lello (Where J. K. Rowling inspired to write Harry Potter)

• Avenida da Liberdade

• Train Station São Bento

• Sé do Porto

• Ribeira do Porto

• Cais de Gaia

Night Life: Here: Rua da Galeria de Paris

To eat (in the North there are plenty of excellent food but in Porto the typical dishes are strong and not everyone likes it)

Even though  you must try them you will love or hate, lol:

Mandatory restaurants:

• Casa Guedes: (great pork sandwich with special melted cheese) and ask for Vinho Espadal to drink

• Kardoso (the most typical dish in Porto: Francesinha)

• Cervejaria Gazela (special sandwich at the afternoon) and ask for: a beer and Cachorrinhos da Batalha

• O Buraco: ask for "Tripas à moda do Porto" and red wine

• A cozinha do Manel: you must come here at least twice and eat: Vitela no Forno; Bacalhau à moda da casa; Filetes de Polvo; arroz de pato

Romantic Escape: Cruzeiros do Douro (one day trip through Douro Valley with meals included drinks excluded)

Grab Funicular dos Guindais (old elevator) from the riverside near Ribeira do Porto (mandatory)

If you go to restaurant "O Buraco" please check if the market "Mercado do Bolhão" still in renovations or it's opened now

Near this, there is an old traditional grocery that you MUST go: Pérola do Bolhão 

If you have enough time, visit Palácio da Bolsa

And...

If you don't have an entire day for the visit Douro Valley (please try), you can go on a Tuk Tuk (they are everywhere and please grab an electric one) and ask for a ride through "Caminhos do Romântico".

Enjoy!!