What is the max # of version history for any given entry? I can't seem to find anywhere mentioning what the max # of versions a given entry can have--I would assume its unlimited (given unlimited DB space).
There is no set maximum number of versions an entry can have, assuming you have unlimited database space.

Take a look at the source code in the EntryRevisionsService for more information: https://github.com/craftcms/cms/tree/master-v2/src/services/EntryRevisionsService.php#L148