Hi, I'm glad to see a new update and thoughts on project roadmap!
Here is what I think - Instead of turning game into some sort of Galactic Civilizations (that has resource gathering from "captured points" and "Non-aggression agreements" BTW), I would better stay away from "strategic concepts" and stick with "tactics concepts", because there is a word "tactics" in the game name :) Since you decided to develop it on your own, what you've described would take years to implement and debug, while tactics part is already in a good shape and just needs polishing.
Another good reason to stay away from strategic elements is that most players expect strategies to be MMO these days, that requires expansive servers. You gonna need to add a huge story line to keep people solo playing strategy with AI (currently I finish campaign in two days or so). What's a cheap way, you would ask - multiplayer will turn game into a sort of "chess" that folks can play over and over againg, making new... tactics! A simple peer-to-peer multiplayer doesn't need any anti-cheat complexities and will free up your hands for more challenging AI coding, rather than balancing boring economy math...
Also, be careful, your strategic part may overlap with these Russian guys, and they are solid from implementation stand point. So Instead of racing with them, I would recommend to stick with "strong fast-paced tactics PvE & Coop & PvP matches". BTW, take a look how they did close-combat and weapon range circles. Another good thing to implement is bushes to hide in. If enemy doesn't see you entering a bush - you can stay there safe unless they come too close and they see you. That's where your new silencer will shine! Bushes may require to turn Middle East to South America, where bushes are more common, so if you not planning this, you may add wardrobes or dark rooms for same mechanics. You also may want to look at this and that project for some good tactics ideas, even though they are not turn-based.
As an option, thinking out-of-the-box on how to make game more distinctive, you may add more character tweaking parameters that will drive his behavior at battle... even in old XCOM characters did fancy actions during panic, and you may bring it to a new level by chewing previous player decisions with Machine Learning... that eventually turns your team into a well-trained AI, that can be picked as an enemy when you start a new squad, "making player fight with his shadow".