Some factions don't seem to care about certain theaters. I don't recall getting any big hits against the Mughals or Maratha from conquering territory in N America or Europe, but they sure cared when I started taking territory in India.

They don't seem to care when you capture rebel territory, but I haven't done that much so it may vary.

They definitely don't care when you expand via trade/purchase. Buy all you like, you won't see any penalties there.

Diplomatic modifiers degrade over time, usually about 1 point per year, so if you wait between conquests the penalties won't get so bad.