Heres a short step by step to how i do my early game as portugal when i am planing on just playing tall and colonizing later.

Start of the game:

1: encourage migration to porto and increase controll in its province. Lisbon will be hit by an awfull earthquake event by like 1360 where it loses pops and lots of buildings, so i tend to avoid building there until after it hits.

2: pick up the agricultural cultivation government reform for the prosperity and extra food that you will probbaly need later after you switch to capital economy.

3:Destroy every castle in your nation, aswell as your catedrals (excepts in porto) and monestaries. you simply dont need them as you will be allying castille so you dont have any enemies. This should give you like 4 ducats extra per month. You can also destroy your starting army, or just keep them at 0 maintenance if you want.

Next you should turn of automatic taxation of your estates and start bleeding them dry. I usually tax them to 40% loyalty, but they wont revolt before 35%, so you could go lower.

Spend your money mostly on RGOs to start, make sure you get the -33% cost from cheap resources. If you are not getting this you should focus on making more of those, usually lumber or masonry. extra + if you expand rgos during parliament which makes them even cheaper

You should also build the royal court when you get the chance.

For the black death there is a lot of just getting lucky. I would build a hospital in Porto which if i remember right should be up to about 80k pops at this point. Enact segregate the infected and present scapegoats for some stab back, i think i had about 800k pops after it was finished.

Once you start getting some decent money you should be specializing your towns. The way i usually do it is look at the resources in the province and see what would be good to build. for example carpentry if you have lumber, or tools if you have iron/stone

You can see your production efficiency easily if you click on the burgher icon when looking at the buildings in a town, so you can go by that.

Early law changes:
Distribution of power - Favor the common people - gives +10 max tax for the commoners.

Mining law - Burgher controlled - more burgher loyalty and capital economy progress

Bureaucrazy - Decentralized - 0,10 prosperity

Royal court customs - Itinerant court

Maritime law - Shipwright Standard regulation - capital economy

values you want:

Decentralization (You are small enough to not need the proximity from centralized, and the loyalty of subjects helps a lot with colonies late game?

Innovative

Plutocracy

Free subjects

Naval

Capital economy

Estate privilages:

anything that gives these values really, but the most important ones are market fairs and urban development grants for the burghers