I think you are making the mistake a lot of us make in that you haven't really determined what you want to get out of your railroad and come to terms with your space limitation. Take the time to think about what you want out of your layout in both the near and long term. Once that is done, come up with a design. Your space limitations will most likely force you to make decisions on what is realistic. At that point, start building.
My advice - lose the reversing loops. You'd be surprised at what you can fit in if you limit yourself to 3 or 4 feet around the walls. If you want to turn a train why not do it like the real word with a wye on a peninsula?
I have roughly a 20x20 space and I'm doing a layout that is 4 feet wide and have plenty of room for an upper and lower level as well as a connected branch line on 2 of the 4 sides. While your runs wouldn't be as long the idea would be the same. You can even elevate one level for better visual appeal. This is a preliminary version so you can get a visual using RRTrack software. I'm using Atlas track and switches as that's what I used on my old layout:
The space in the middle is where the stairs come down which is why it seems so open. I will have between 30" and 35" of space to stand between the layout and the steps. There is also a 4' area between the outer edges of the layout and the walls on 3 out of the 4 sides. The angled area in the lower right hand corner will only be 18" wide as that's where my lift-out section will be. I will make them pivot and rotate to open like a door similar to what John Coy uses on his layout (do a forum search or go to YouTube for layout videos). Ignore the two double-crossovers. Not sure where I will place it but there will be only one. I have two there for track spacing as I design.
Around the walls isn't doable for me as I have a crawl space, furnace, hot water heater, etc I need to access. This is why I will have such a long area to be "lifted out". I settled on 4' wide as I want to be able to reach everything by hand while standing on my own two feet. I'm only trying to give you ideas not convince you of a different approach.
Bottom line - determine what YOU want on YOUR layout and then build it! 
You're the only one who needs to be happy!
-Greg
