Good Castile start. How to proceed?

Year 1453 in my Castile game I just got Iberian Wedding (Aragon and Naples in PU). I have Isabella 5/6/3 on throne and she is 19 years old. I killed Granada and have Portugal as ally but not RM. Navara is vassal. I want to colonize and be decent army. Ideas? I thought about 1.Exploration 2.Expansion/Quantity? Should I feed Aragon with North Africa? Which area should be priority for colonisation? Caribean? South Africa? I want to cut England, France, Brittany, Norway but I dont need to do it ASAP.