Improved balance.

You yourself said in the neighboring thread that Heroes should have some resemblance to reality, i.e., resemble a military strategy. Paying troops, it seems to me, is exactly what is needed to improve the Heroes. It is not a complication, it is just not suitable for some maps. You can make a button in the menu before the game and in the editor to give players a choice of whether they want to play with troop payments or not.
By the way, in the games that were the progenitors of Heroes, there were only two resources: gold and crystals. Therefore, I also suggest making three resources: gold, wood, and ore. Then there is no need to worry about the lack of resources for construction.
Regarding events, you may be right, it is unnecessary.

It is a complication, at least because the maintenance costs will not be displayed in the income graph in the kingdom overview, and thus, the player will constantly have to calculate and keep this figure in mind when planning ahead.

Approximations to reality are good only as long as they do not spoil the gameplay. In Heroes 5, a major drawback is the low turn dynamics, i.e., the long turn duration in real time due to the 3D map and inconvenient camera, as well as more complex battles, slow animation in them, and the starting deployment phase. The low turn dynamics is further aggravated by the low game dynamics due to the features of the maps and cities (city levels in H5 allow you to reach the top levels only by the end of the 2nd week, and in H3 - by the end of the first). And the introduction of a maintenance fee, which requires a certain amount of time to forecast the economy, will further worsen the situation. While many players appreciate Heroes as a strategy precisely because of its simple economic model, without unnecessary complications.

P.S. Autoplay does not really save the dynamics, because the features of the H5 maps imply breaking through with losses close to zero, which autoplay cannot provide (in H3, you could give up half the army and get a wyvern, super artifacts with +6 to all stats, or just a lot of resources, allowing you to compensate for the losses by reaching the top levels early, which H5 does not have). Simultaneous turns do not work on hotseat and in single-player, and are disabled on dynamic maps from the first days.

Added after 1 hour 6 minutes
Regarding reducing the number of resources: is this a copy-paste from Heroes 6? This idea did not work there. And the complications with maintenance do not come from resources in general, but specifically from gold (unless, of course, you introduce payment in resources).