I have a few questions:
1) How can I see approximately how many griffins, dwarves, etc. are in castles, dwarf dwellings, etc.?
2) How can I make it so that during a battle, when you hover the cursor over an enemy, the average damage that your unit will deal to the enemy is displayed?

1. Go to the object, in the message click cancel, and right-click on the object - it will show the approximate number. You can immediately see the number of castles/dwarf dwellings/medusa dwellings, but you'll have to exit the unit list to do so.
2. You need to go to the settings menu during a battle (the button with the computer icon) and enable the "unit information" option (either all or just spells). Along with the information, the damage will also be displayed.