My path has always been:
1.) Attack Sunda
2.) Allied Kutai (so they don't get attacked by Brunei)
3.) Fabricate claim on Luwu+Makassar
4.) Attack Luwu+Makassar
5.) Fabricate claim on Brunei
6.) Attack Brunei
7.) Focus your trade in Malacca so you can justify trade conflict against sumatran power or malayan power
Also, check your Sumatran and Malayan neighbour all the time and ensure them not grow too big...
A Sumatra nation that has all of its neighbour provinces is pretty terrifying (mostly due to gold in Pagaruyung province, might want to make that your priority target)...
Even worse situation would be a unified Sumatran allied with unified Malayan (such as Malacca that has conquered Kedah and Pattani), the only force that forced me to restart...
Humanism is good idea group if you want to conquer fast without increasing autonomy (even reduce it almost as soon as you conquer them)...
Religious also good if you don't want to forge claim or justify trade conflict, especially against Ternate and Tidore because you have no neighbouring province with them and they are too small to have enough trade power to justify trade conflict...
Expansion or Exploration also necessary because most of the region is colonize province, but you can take them as second or third, but remember that later you get them the more land available for European to colonize...
Anyway, once you finish do this, you've ensure the archipelago as yours, can formed Malaya, and the rest is up to you...
But I think my strategy isn't the best one because there are people that have done a lot more much faster...