HoMM3 HD is a mod (add-on) for the game Heroes of Might and Magic 3.

...
Question: Is it necessary to create a window that requests confirmation with information about the number of creatures and resources? (I don't want to). How likely is it to accidentally press a hotkey or button?
If we don't create a confirmation window, as an alternative, we could implement a quick undo for purchases using [CTRL]+[Z].
What do you think?

If you click on the icon with a key combination, you won't make a mistake. However, in that case, you'll need an additional key for both troop selection options. Or, you could use the right mouse button with a key combination – then you definitely won't make a mistake.
By the way, you could create a hotkey for quickly exiting the troop purchase window in a town and returning to the main interface.