Dude...I'll be honest, I did not read through all of those walls of text. But here's my general advice: Before you concern yourself with concept art, AAA-graphic effects and whatnot, first of all make a gameplay prototype in the engine of your choice. I'd use UDK since its fairly easy code-wise from what I've heard but I guess you can use Cryengine too.
Then, when thats out of the way you can still make it look pretty. But coding is always the most difficult part and nothing's worse than sitting on tons of beautiful assets and levels with no working gameplay feature to go with them. Trust me, I know...
Quote: i am unsure they can handle the classic "open plan" level design and "old fashioned silver era" gameplay i am after.
...well, like I said gameplay features depend entirely on your coding skills. Its even possible to make a 2D-sidescoller in Unreal Engine if you know what you're doing. And Level design doesn't have much to do with the engine. Some handle Terrain and extremely far view distances better than others, but no engine cares about whether your level is linear or not.
(Except for some AI features maybe - but that's where your coding skills come into play again)