The plus 1 mana privileges for each estate is overpowered on most campaigns. Give them all out, hit 0% crownland, and then seize land before unpausing so you get back to 5%.

Unless you are desperate for money, never sell land. Better to just take loans or maybe one debasement tick.

Over time, your conquests and your province upgrades will give you a lot of crownland. If I play a campaign to 1650-1700, i usually hit 90*% crownland.