Some questions i have

1. Certain terrain types increase or decrease the defense of the unit located there. For example the center of a city (with the name) gives +2 defense, while other city area's, factories and airfields give +1 defense. Mountains and forest give +1 defense and rivers give -1 defense. Infantry units with an engineering special force can build fortifications, like trenches and bunkers. These give a certain amount of defense aswell. If a general with Elastic Defence is positioned on one such fortification, the defense it grants is increased by 2.
2. Probably yes. I have not purchased a general with medals, so I can't check it just yet. But looking back at previous games, you can probably resign a general and get about 80% (I believe it was in previous games) back from the original cost.
3. I am not sure how tech is calculated, but based on the icon, I am guessing that factories produce tech.
4. Moral has a scale (probably 0-100), performing certain actions will decrease or increase moral. The exact triggers are unknown, but the tutorial shows a few. If you surround a unit with atleast two of your own (one on each side) the moral of the enemy drops. Dropping a paratrooper behind an artillery unit and attacking it, decreases the moral if the artillery. Defeating enemies has a chance of increasing moral, etc. There are four levels which display's moral: high (golden symbol + 1 arrow pointing up, increased attack), regular (no extra benefits), low (light blue symbol + 1 arrow pointing down, decreased attack), very low (dark blue symbol + 2 arrows pointing down, even more decreased attack) and chaos (question mark symbol, can't do anything like move or attack, happens at 0 moral).
5. Annilihating is when you destroy the entire unit, not just one bar. So the unit is gone.
6. A city tile is any city that portraits as a city (which give either +1 or +2 defense), though maybe factories and airbases might count aswell.
7. The line above the rewards in campaign missions show the accumilated supplies during that mission. These supplies are gathered by completing the secundary objectives. The total of these supplies are the supplies that you get with the last mission of that subcampaign.
   - For example during the battle of Poland in 1939 Western Front, there are three missions, "Blitzkrieg", "Battle of Warsaw" and "Case White". Where "Case White" has a star next to its name and is not required to continue the campaign. During "Blitzkrieg" and "Battle of Warsaw" you can collect a total of 150 supplies each. So if you finish these missions with all secondary objectives, you start "Case White" with 300 supplies, making the mission easier to finish.

I think it is very similar to original GoG..
It wasn't possible nether to refund the medals spent on generals, nor to upgrade them. We could upgrade our Commander though. It is a pity they didn't give us one in GoG3.

So, our choice is really crucial right from the start...

Yes, that is very true. No medal refund, no reliable way to farm medals, and no mission that gives medal. Buying a wrong general can be fatal for f2p players.

Gog's brutality really makes me afraid of what's to come with gog3

With the new war master video opening up the
possibility of the aliens/terrorists coming to figth I'm scared considering how tough they are in the wc games

Annihilate is actually when you destroy "one unit" or bar of health. If a double infantry is close to losing that bar hit it with a tank. Even if you don't kill the entire formation, you killed a unit technically so you get the 60% chance. This is very crucial to timing attacks on various units since so many can get an "attack after annihilating"

Perhaps it was just a rare occurrence and the ai just forgot to attack?