I started out the same way, went from years of WW2 to DCS. Personally I found the bfm to be similar in a hornet to ww2 aircraft, but needing more precision. What carried over for me were the visual cues, understanding the fight geometry, gunnery, recognizing overshoots, scissors, 1c vs 2c fights, difference in energy states (though I had to relearn the cues for that). Pretty much all bfm basics haven't changed in 100 years, just the speed and altitude where they happen. what was new to me was the importance of maintaining that right corner speed, operating the avionics and countermeasures, breaking the habit of using some ww2 specific tricks that don't work with jets, and needing to react to cues faster than in ww2 sims. I struggle the most in BVR engagements, missile evasion, that kind of thing, because there is no analogue in ww2. boom and zoom only works if it's guns only/they are much slower/underpowered/don't know you're there, and you break off before you get in front of them. There's a saying for the hornet, "go up to blow up". the hornet doesn't do well in the vertical in most situations. against most fighters downhill is the way to go. In a fox 2 environment you definitely can't run. pretty much any aircraft in the game will be able to get nose on and fire before you get out of range. best bet there is get your nose on them before they get nose on you (I know, not super helpful), or at least keep turning so they can't get nose on and wait for them to make a mistake.
As for 2v2, with a human wingman communication helps a lot to avoid blue on blue. with AI best advice I can give is always keep an eye on where they are. there may be better ways I don't know about. I don't really know the inner workings of the iff.
The missions that helped me were the single missions for the hornet, the 1v1 bfm against the su-30 then the mig-21, moving up to 2v2. and for fox 2 the weapons qualification. I created a few of my own missions that helped a lot as well. Don't be afraid to jump in the mission editor and create your own setups for air to air and air to ground. you can control the opponents skill, relative position, loadouts, and even make them ignore you if you like. Just drop two fighters near each other, make one red and the other client, and go from there. Fighting AI will get you the basics but it is a huge jump going from AI opponents to human ones, it pretty much felt like starting from the beginning again.