Let’s come up with new “war machines.”

That's definitely an overdoing. It's better to have original items for each faction than just generic rams and towers, which, by the way, don't really fit the style of Heroes.

P.S.: And could it be possible to make it so that a hero with the advanced ballistics skill has the option to buy not just a tent, a ballista, and a cart, but two ballistas or two tents. And with expert ballistics - three ballistas or three tents...