This isn't exactly a question that can be answered in the way I think you're hoping, but I hope I can provide some insight.

Messages were sent just as you would think - via letter or a messenger himself - so they did indeed take a while to organize. From the time of the proclamation of the crusade, participants had to gather funds, soldiers, and various other materials for a roughly set meeting date. Using the First Crusade as an example, from the Council of Clermont in November of 1095, the crusaders had a bit less than a year to prepare for the designated departure time (though obviously kings (or princes as the phase in which the big royalty left was called) had more leeway) of mid-late 1096.

The meeting point after setting out from Europe was naturally Constantinople, and due to the differing schedules of the princes, they left at different times and went the route they saw most fitting. There wasn't much organization beyond these vague target dates, and as the Peasants' Crusade showed, this very rough organization was all for naught if a group arrived much earlier than the others, as they were ferried across the Bosporus by Alexios and subsequently slaughtered.

The organization (or lack thereof) as the crusades progressed provide rather solid proof that the ways in which organization was attempted were simply bad. The princes of each later crusade rarely (if ever) truly organized with fellow princes to the extent that would see victory, but whether out of want for prestige or what-have-you, it's up for interpretation.

I suggest checking out Thomas Asbridge's The Crusades: The Authoritative History of War for the Holy Land.