There are no such restrictions. Theoretically, you can sync hundreds of calendars, so I guess there’s another reason why some calendars don’t show up. Do those calendars have something in common, for instance are they shared calendars?
Sorry if I’m missing something or if it’s covered elsewhere. I had a lot of contacts on a phone running CM11 (Privacy Guard disabled) not attached to any account. I created a Davdroid account that connects to an Owncloud account on which there were no contacts. I expected these unattached contacts (“phone-only, unsynced”) to become attached to the Davdroid account but they didn’t. I ended up exporting the contacts, deleting the data of the Contacts Storage app and importing the vcf into ownCloud. Maybe I had’t picked the correct account to sync (if there was one; I haven’t been able to repeat the steps) but even so it could be made more obvious that the user has made such an error.
Also the FAQ link in the app doesn’t point to the FAQ but the configuration.
Similar behavior is also described at http://a3nm.net/blog/davdroid.html (“1. Warning about migrating existing data”); so it looks like you really took the only possible way
Moving contacts between accounts isn’t the task of DAVdroid (which is only CalDAV/CardDAV sync adapter and not an Android address book or event manager). Please use an appropriate app for this (or import/export).
OK, but I suggest documentation could reflect this situation better.
@dalb8: Agreed. I think this should go into the FAQ.