I will answer both of your message into this one so I'm not creating a ton of new messages.
The scale and what I decided for my campaigns and my map is around 4 km per hex, but it can vary on the scenario (thinking about the eastern front especially where distances are just huge) so I tried to cut the scenarios into stuff that still make sense but that also tries to respect the scale at all point. So for example small countries like England, for the Sea Lion scenarios I cut it into 2 maps of 70 x 45(south) and 45 x 70 (north).
Now about units, well the thing is once again, due to the various editors you are able to give the game the scale you want. But for my campaigns / scenarios, it's at an operational level. Few hundred kilometres not more. So for units it's often divisional level but can also be regimental level. But once again, as you can edit or create anything, it's up to you to decide when making for yourself.
About combat, it's pretty straight forward. Final damage = damage type (soft/hard/air) - enemy unit's armour - terrain modifier.
But it does not apply to everything. CAS / ground attack planes will ignore 50% of the armour. Strategic bombers will ignore 100%. Submarines deal a random damage value between 0 (miss) and a max of its hard damage value, to simulate the effect of a torpedo, because hitting does not mean sinking.
Also the health point percentage of the unit will modify how many damage it deals, a weak unit won't deal as much as if it was full health, makes sense, less people alive / ready to fight.
So all in all, if you want to know every little detail I'd advice you to take a look at the official guide I wrote and look at the combat / damage section (it's on steam).
About moral, I haven't came up with anything yet. I'd like to add this. Still figuring out how though, I'm unsure of how it will work and what effects it will have etc. If you have ideas, once again, I'll listen.
That's also the thing, to finish answering your first question, I came up with an idea of making a game, and I just kept / still keep adding up on top. The idea I had for the game in the beginning and what the game is right now are two total different things. I tend to make everything optional in the settings though (such as the supplies), so everyone can enjoy the game with the options he wants.
Ah ! You asked about supplies. Well I guess I'll explain that right after telling you that no, I am not going to add planning (thinking about HOI here in particular) because the game really is meant to be played in turn by turn and each unit individually. Just a real wargame where you have tons of counters and when it takes a long time to complete a turn. Not because it's a hassle and it's painfully long, but because you need to micro manage every move, every supply, etc. That's what in my opinion gives the game its flavour, not having everything automated, and you still have control over it.
About supplies, AGAIN, lol, this time for real. There is a simple and a complex mode. Simple mode is when you hit resupply, it resupplies regardless of the circumstances and where you are on the board, encircled, not encircled, basically you resupply without any condition. Now the complex mod that I added like 2 days ago, this goes deeper. There is a supply line created from every unit to the closest city. If this supply line is disrupted, meaning an enemy unit in the middle, you won't be able to resupply at all. Now if you're not on the road but somewhere in the plains or in the forest, you won't be able to resupply at 100% efficiency, I think it makes sense a truck will have a harder time getting to you in the middle of the forest, than getting to you on a normal road. I haven't added a limit supply number per city yet, that's yet to be decided, by me and the players. Like each unit has a supply consumption value and each city can only produce X supplies and so if you have too many units per city well they could not get as well resupplied. For now, it's not in the game.
about C3I no, don't think this will ever happen.
About your second message and the name, yeah, I get it. I'll rename it to something strategy warfare or something more generic.
Thanks for your questions ! I hope I answered with enough details. If anything, ask again, or visit the guide :)