I've just started a Poland campaign but Portugal is next on my list, definitely going to give this a go to see how it affects Castile.
As much as I love EU4, one of my only gripes is that Spain always become so poweful towards the end of every campaign with their vassal swarm.
You must do what ever it takes to keep even 1 Muslim province of Granada in Iberia. Spain will never form with it's powerful ideas and missions.
Break the truce with Granada of all it takes. As long as Granada isn't allied to Morocco it will be easy first war.
Further advice regarding Portugal
-Try to take Morocco's provinces in the Seville trade node.
-Feed all other territories to a new vassal in Morocco which you will create.
-Do not go all out war with Morocco alone, if Castile cannot help.
-If Aragon has rival Castile but not you on the first day of the game, ally Aragon.
-Marry to England and as soon as the timer expires cancel the alliance. You cannot afford been dragged to wars with France.
-Make France your ally at all cost.
-Get Exploration & Expansion ideas first, followed by Quantity, Influence, Quality.
You will have a lot of huge colonial vassals making gazillions from trade.
-Maintain a balance on tech. Better spend some Monarch points to improve Porto & Lisbon than having to pay thousands to corruption due to unbalanced research.
Stock pile to maximum before new idea group is unlocked. But spend military points on new tech if you go to war and you are behind.
-Colonize Canaries asap. Followed by the West African province. Attack one of the natives in North side of South America to get a foot hold
Then continue to the 10 development provinces in Caribbean. The islands north of Colombia will do. Expand with 2 colonists to Brazil and 1 in North side of Mexico.
In Brazil there are natives. Attack them and annex them. They will speed up your claims to Brazil. Make sure you colonize to the area around Rio, since there is a mission.
In Mexico, colonize the coastline moving North to Louisiana. Ignore North America completely.
Give subsidies of 2 ducats for 400 years to Caraibas. Your colonial nation in the Caribbean. Help them to gain foothold in Cuba & Haiti & Jamaica. It will be one of your strongest colonial nations and vassals in the long term.
Followed by your Mexican vassal when you gobble the Aztecs and Maya on it's behalf.
Use your army to purge the areas you colonize from the native. The population is low. 500-1000 ain't worth the trouble.
Pick the extra colonists option when you open the fist colonist.
Here you need to do asap to have open the 2 modifiers from age of discovery. The one that is special for Portugal giving extra colonists and the one that gives +3 development (1/1/1) to new colonies.
With those 2 plus the other modifiers you will out-colonize the rest 3 to 1 at the start. Paramount to get more colonies. Hence Humiliating vassal and big capital need to be done the earliest as possible.
If Temcen is alone, make it rival and go for humiliation & money. The easiest to pull, since you do not want lands etc and it will disappear fast.
While colonizing and not at war do not train your army. Set maintenance to 0, and pay the penalty to have more new colonies building than colonists.
When you open south Africa with your explorer. Start colonizing there. You will need 5000 troops stationary in the area with full maintenance by then.
Your colonies in Africa & Asia should be assigned to trade companies.
Make sure you do not purge the African colonies. The 500-1000 natives areas are OK to do, but the big ones with 4000-5000 population a big no no.
They will boost the colony for free.
Expand to the islands east of Madagascar, Australia, Timor. Do not have attached neighbour area any of the countries there if you plan to attack them. Especially the island nations in Philippines.
Expand to California, use your European armies to break apart the Aztec nations and when times comes, go for the "Concede <X> colonies" instead of picking the areas.
Only if a nation is big enough you have to pick the areas. Start with gold.
-Advisors. Keep them balanced until Tech 5 where you get the first idea. Then push everything to Administration, until you open Quantity. When you do so, move everything to Military until both Quantity idea group is fully unlocked. And you balance them like that between Admin & Military all the time.
-Use your merchants efficiently. Take the one out of Tunis and post him to Seville. Use 2 light ships on Safi node the rest on Seville node.
When you start getting Merchants from colonial nations & Trade idea group (it worth to pick it on Portugal) set routing properly. Eg on east Africa steer trade through Ivory coast not Alexandria by setting it manually.
Hope that helps. Wars etc in Europe do are you please. Pray France remains Catholic and not go Reformed.
If you fight Castile with Aragon, take Seville & Cadiz and the Canaries. Break the country apart by releasing nations. (Leon etc). Pick also the colonial nations in the peace treaties if any.
And do not forget to embargo your rivals. On Seville node you can screw Morocco, Granada at the start. Tunis, Castile and anyone else later on.
