That would work but I don't think it is the best idea. You really want exploration and expansion to be a colonial power. I would probably focus dip, take exploration then expansion second. Get Navarra and Galicia as vassals, probably even a released catholic granada as vassal/ally too, and use them to eat Castille and Portugal's coast while you take the islands and core them yourself to extend your colonial range to the Americas. You can probably shut them down quickly only coring 4-5 provinces over a couple wars yourself. While doing this, annex your starting vassals to keep relations manageable. It's ok to be a few over your limit for awhile.