I prefer the WebDAV File-System, other prefer dokany as filesystem. As you want to deal with very large files, You must use dokany (which is the standard configuration), as WebDAV comes with some limitations. Other than that there is no reccomendation in copnfiguration. It depends strongly on your needs and usage. Just try it 
no.
Cryptomator itself has no limitations. The limits are primary your disc space and your online storage space.
As far as I understand you only want to have online backups for a huge amount of data. I reccomend to read this thread: How do I use Cryptomator without local sync?
The iOS app and the Android App needs to be purchased. The desctop apps are provided for free. The licensing is typical for iOS and Android. You purchase once per Appe and/or Google Account. If you have more than one device connected with this account, feel free to use the cryptomator apps on all these devices.
Not as far as I know. If you are looking for Enterprise solutions, please check this page Enterprise
If you are looking for a enterprise server solution, please check this https://server.cryptomator.org/en/