1. yes
2. yes, devs have talked about how they're focusing on realism a lot more than RO2 did
3. unknown
4. CryEngine 3 is used, so far all their maps are 1:1 scale of real locations (Juno Beach revealed as one of the maps), made by the DH devs
Well FE would have to be pretty damn spectacular and done very well to sway me over to pay for it.
To be honest, I found Darkest Hour lacking in many many things and couldn't stand playing it. Sure it had a lot of content going for it and DH tried very hard to bring in some unique things to the gameplay, but despite some of the things RO1 did differently from ROCA that I didn't like being changed, I still liked RO1 and when given the option to play DH or RO1 back in the day, RO1 was always my go-to.
DH was just "Bleh" for me.
I do like how this FE is going to focus more on the British / Canadian Forces though, as that's certainly more unique for FPS's, especially for WWII. The other thing that bothered me about DH was the heavy focus on the US vs. Germany and it's also why I don't care much for RS, as it's the same US weapons and such that are found in every other WWII FPS out there. What got me into RO was that it was the Soviets, not the US.... ie: a different set of battles, using different weapons and such.
There were Canadian/British in DH but 90% of the matches I ever came across were just US.... then map votes brought you back to more US maps and over and over.
I'll just wait and see what FE has to offer. I don't see anything new on the site except modeled weapons and a few map screenshots.... which doesn't say a lot. I've seen plenty of mods and stand alone games with much of the same which never materialized.
So in short, until Festung Europa is actually released, it's a non-issue and all of the talk in the world about how great it will be is meaningless.