I often have a crusader state, usually I take Antioch, Jerusalem and Acre.. maybe Damascus too, depends. If you are not at war with everybody in europe, I found a full stack in every crusader city is enough (and economically affordable) to keep them from rebelling, you will need it anyway as you will probably get besieged every 3 or 4 turns. The only way these cities rebel on me is when the enemy is successful in sending a couple of spies in who stay for more than just one round.
As France I had an additional all cav crusader army composed of mainly Knights Templar and horse archers that patrolled my borders and served as a quick response force. Was especially handy for ambushes on various Mongol and Timurid stacks: attack and then retreat and retrain in your castle.