Okay so one of the reasons you mentioned you were on this forum is to get feedback, so I will offer you some if you are interested in hearing it. It refers specifically to this.
As the difficulty increases, various modifiers (dodge chance, hit chance, debuffs, stats, etc.) will change.
In addition, with increasing difficulty, enemies will use new abilities. That is, their intelligence changes. Also, the number of mobs for some encounters will change.
Changing modifiers, increasing the number of mobs per encounter, and enemies using new abilities are all great, and what is to be expected of a higher difficulty. Let me just give you some advice, and if doubt the merit of said advice feel free to ask any Codexers on this thread and I am sure they will agree.
Changing the types of enemies you see at different points in the game (as long as it's logically coherent within the game world) is a great way to increase the difficulty while also making the higher difficulty, and the game in turn, far more engaging and interesting. Believe me, it feels way better to run into chaos spawn variant number three with its stats and abilities, than it is to run into chaos spawn number one with buffed stats and abilities, even if mechanically it would feel the same as chaos spawn number three, if that makes sense. Instead of giving new abilities to the enemies that were in the encounter on normal mode, why not add a mob that has said abilities to that encounter in addittion to the other mobs in hard mode? Obviously this wouldn't work if it doesn't make sense for said enemy to be there, but when possible to implement it's great, and in those situations, it would be awesome if the team did a reskin of that enemy in a way that would fit the current encounter at the time, just for that harder difficulty. This has the added benefit of encounters on higher difficulties getting more tactically complex, versus just a higher stat check, which is typically what higher difficulties are in most games (although you did mention plans to add new abilities to mobs in higher difficulties which would be taking steps to avoid this, so that is good to see). This also doubles as an easier way to make more complex encounters. Many times it feels that developers struggle to make encounters complex at higher difficulties because encounters have preset unit compositions/types, and for consistency reasons, units between each other need to have the same stats (they don't NEED to, this is just a common thing in most games). By adding new, more "advanced" mobs that would usually be seen later in the game, with their own special abilities that require special tactics to deal with, to these encounters, you can create a higher difficulty encounter that is actually engaging versus boring. Trust me when I say, this adds a ton of replayability to the game and it's the type of care/attention to detail everyone, even the more normie gamers, love to see, and I can't imagine it requiring too much effort.