...starting with my humble experience in TCG games and the obtained with several hours of playing this great wwii
Eh? Have I seen that name before? GusGus... hummm.... are you new here?

(just a joke of course! And your English is excellent)
I agree that Coalition also needs "nerfing" since the current British Rush decks are overwhelming. Oddly? OP Jack is the #1 way to wipe them out! You get 3-4 units with 4 & under Defence (like Northunmbrians, Tortoise, Monty...) and it can really turn the tide! But again it comes down to pure luck of the draw...
Fear: Lower by X by unit type sounds reasonable, once Jack is reduced a bit, but lowering "to X" is far too powerful, unless maybe it goes back up at the end of the turn? Or the end of the opponent's turn? It's HARD WORK getting that defence up! This would help counter some all-infantry and all-aircraft decks.
Battlefield Environment: I think that could be interesting, but more for a Mission or a PvP Tournament? It would be in place from the start, not a card to be played I think:
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Mud for example could make all tanks Slow and reduce their numbers -1/-1?
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Jungle could make Aircraft less effective, -1/-1?
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Night battles could give all units -2/+3 when deployed (as a buff so Promotion or other things would remove it)
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Minefields: hit all advancing Infantry with -2/-2 & tanks -1/-1 ? when they move to the Front line, unless they have some mine-clearing equipment OR a Tank went before them, 'clearing' a path for the next unit (but not the one after). Mines played a HUGE roll in WW2, yet they barely exist in this game, eh?
As for Fortune & Enigma: I've been thinking that being able to
"carry over" a single card to the next draw would be really fun!

Of course the opponent could see it too, & prepare! If un-played it would return to the Deck, and this couldn't be played 2 turns in a row, and would count as one of the 6, not be "extra". It would be optional of course, if the remaining cards are all crappy, just don't save one!
This would give players some
real flexibility in the draws, and add a LOT to the thinking part of the game, thus reducing luck. Balancing it for the AI would be nearly impossible, I think? So strictly PvP. And since both sides can do it? it won't further un-balance things much...
It would
greatly improve several annoying parts of the game:
- Dead Draws: at least you can keep one item/order for the next turn. Better than nothing!
- Bad timing: got Jack when opponent has no cards in play (like going first) or there's no place to put Bombe? Carry it over & hope next turn works better.
- Enemy stole much of your AP with Busters & Scorched? Tossing away cards you'd love to play? At least you can keep one for next turn, thus slightly lowering that problem.
But mostly? It would be
MORE FUN! 
Cheers!