Yes it can, however you will want to have one central CMS and all players connected to it for easier management, certainly not one CMS per one player as that would be an administrator nightmare 
It’s hard to say, as it may highly depend on the content that should be displayed on it - I’d recommend that once you have the CMS set up, create some layout and test it against your old computers to see how it runs on them.
If they are running on Windows XP, then that could potentially create some problems, as you would not be able to install IE11 on them and therefore Xibo couldn’t use emulated IE11, which in some cases may cause layout playback issues.
We do not recommend it - Can I run a Xibo Player on my Raspberry Pi (all variants)