How do I Crusade?

[_Tristan_]

Fact is that the troops on Crusade are inviolate to other Catholic kingdoms much like any Catholic cities are inviolate from same Crusading armies (though there is a workaround for this : separate your Crusading general from its stack, have him leave the Crusade, siege the Catholic city, then have the stack join him at the walls and have him join the Crusade back... and voila !!)

Rewards for success:
1. Florins from the Pope.
2. Experience for 20 or so troops. (As Unread said)
3. Not sure but I believe you also get extra troops.

1 - True (depending on the number of generals/units having joined the Crusade, the more the better the reward...)
2 - Experience (one chevron per successful crusade is given to all Crusading units) is not limited to 20 or so. One good way to provide experience to all units is to have as many of your generals and units join the Crusade in the turn when you're ready to assault the Crusade target (every unit that joined in this way will gain the experience bonus from the Pope, even if it didn't take one step towards the target...). Hence no risk of desertion and no need to walk over half the world to gain experience...
3 - Nope : no extra troops on completion of crusade but during the crusade and while it lasts you have access to a larger and better-quality mercenary pool.