Uhh I love crusades also - the thought of going through a lot of enemy territory, taking an objective and then fighting for survival far far away from home, often without any immidiate reinforcements. When I sometimes find MTW a little too easy I usually try to make a crusade succeed against all odds.

As to the "how to", it kinda depends on who you are and where your target is. As you cannot rely on available sea transport, crusades from western Europe to the Holy Land can go through Hungary/Byz or Africa. Crusades to eastern Europe and the steppes can usually choose from a host of routes.

In general though, I always try to spy on the provinces that I plan to go through. Failing that, I fall back on the experience of launching God nows how many crusades these last 5 years. There are "good" provinces with zeal above 60% and there are "bad" provinces with less. There are also "very bad" provinces especially near Constantinople with *very* low zeal (5-10%). In general you'll gain troops in good provinces and lose them in bad. Then I consider the target. Rich eastern powers will usually have a lot of troops, and can launch a massive counterattack should you take your target. I always plan to end up with at least 1.500 troops in the end (normal unit size). Not counting peasants.

As you not only pick up the local garrison, but also gain bonus troops from "good" provinces, you can estimate a rough 300-500 men influx there. You'll lose 150-250 in bad provinces, and maybe double that in very bad provinces. Then you can estimate what you need to begin with. I find that I usually end up with too few missile units, so my advice would be: bring a couple more of those.

I usually make the faction heir lead the crusade, as he will be able to teleport home, when a succession is needed. And the experience of frequent last stand battles will benefit your empire. Just make sure there are more than one heir, if things get ugly.

Best of luck with crusading!

/KotR