Yes it is compatbile, though it is not natively supported. You will need to download our separate zip file for your configs, and you will also need to install a worldguard patch that we provide since 1.12.2 is so outdated. Please refer to this page for a detailled 1.12 installation guide.

No, all of the options in the editor for these things build off of other plugins. We have a very small free addon that adds a simple mana/stamina system into your game that will hook with MMOItems, but we also develop MMOCore which is a massive RPG core solution that includes mana, stamina, levels, classes, skills and so much more.

YES, you just need to enable the item updater for said item. Please refer to this page.