Mike-
Sorry to hear about your health woes. I hope you are feling better.
On to the layout. Are you sure you want to go with the double decker helix arrangment. I think I'd advise against it, for several reasons. First, the helix takes up a lot of the space, so you don't get nearly the 'bang for the buck' that it would give you in a larger layout. Secondly, because you only have .9m width the radius of the helix is going to be only 16 or 17 inches (in old money). So the loops are not going to have much clearance, and the grade is going to be steep. So performance will suffer, and maintenance will be a pain. Thirdly, do you really want the annoyance of constructing something that complex for realativly little gain? I'd think long and hard before I went this way.
On the layout plan itself, with all due respect to the TrainClown, I really don't like the crossings (or doubleslips) in the middle of each deck. On any layout, but especially a small one, you want to try to minimize the times that a train passes through the same scene, to make the distance seem greater. With those crossings, you are going to be passing through where you just were all the time. I don't see the benefit other than to turn the train, and even then, you'd only need to have one.
With you space I think I would start with a door layout plan and grow it. Take a look at this site:
Dave Vollmer's N Scale Pennsy Middle Division
(It is having maintenance this weekend, so there may be trouble accessing it)
You've got about the same width, but more than half again the length. Look at the video on his front page. It is hard to believe it is on a door. Imagine it 4 feet longer! He can't reverse trains, but with your extra length I think you could sneak in a cutoff in each direction and hide them well enough to make it unobvious.
If any of this sounds useful to you I'll spen a little bit of time sketching out a rough idea for you to start from. I'm not an expert by any means, but I can sometimes figure what will work. If you could give a clue about what sort of railroad you are after it would help.
By the way, why Fleischmann (good stuff) and not Peco?
Jeff