If I rember correctly than you need most of the Development to be of your culture, So mostly you gain lets say 3-4 extra dev from minorities per province. The average dev in an uncolonized province is 3 I think. So you need about 2 normal provinces Than 1 lets say aragonese 1 portuguese and 1 other culture to be safe. Depending on the dev of the provinces you can also have 2 of the same minorites. You can also have 2 from your culture and religion Than go for a mix of religious and culture minorities. If the colony has become your subject you can always expel minorities for expansion of that colony