For a WC, the first thing you should decide, is : Do you colonize?
If you don`t the ideas are fairly obvious:
Administrative: because mercs are your infinite manpower, coring cost and diplo cost give you tonne of admin points that you will need.
Then you need to know how fast you will expand outside your own faith, to know when to pick your idea that deals with religion. Religious or Tolerance both work perfectly fine, just pick the one stacking with your NI/religion, usually 1st to 3d pick, depending on starting location.
Pick Diplomatic and Influence. Diplopoints can be a real bottleneck, and diplo reputation is necessary for fast annexations.
Plutocracy/Innovative. Mostly for tech cost reduction.
After that, pick whatever you fill you`re lacking. Extra diplomats, military power or policies combos.
Military ideas are very weak for WC, as your bottleneck is Diplo/Admin monarch points, after first 100 years, there should be no state able to challenge your anyway.
Only military ideas that are worth picking are offencive for siege bonus and Aristocracy for extra diplomat.
If you want to colonize, you need to switch your idea order and squize exploration and expansion as your 2d and 3d ideas. The "pro" is that you don`t have to deal with AI colonial nations going rogue and becoming independent, especially since wreaking their mother country now directly increases liberty desire due to high war exhaustion.
First 3 idea group you go for 1 adm, 1 dip and 1 mil, starting with whichever one your monarch is best at.
Unless you use national focus.
