Here's my two cents worth based on what you posted. I believe an around the wall layout would offer the most bang for your buck. Since you want a long mainline, you will probably want to build a double deck layout. You might build the helix around the support post, thus eliminating that as a scenic problem.
You are going to need to use large radius for your curves and #6 switches to accomodate the size of modern equipment. That will limit the amount of operation you can fit into the room. For example, a 30" radius would mean that on your 14' wall, you have bout 9' of straight track between the curved track necesary to "turn the corners". A number 6 switch takes about 12", so 9' minus 2' leaves about a 7' passing siding. Is this long enough for the trains you plan to operate? A yard ladder will take 12" for every switch, so your yard almost has to go along the 19' wall.
Your space is similar to what I have available, though yours is slightly longer. After going thru many designs, and looking thru seemingly endless numbers of plans in magazines, I found an "E" shaped layout gave me the best use of my space.
I believe the most accurate way to see what fits is to use actual switches and sectional track and lay it out on the floor. You can make this work with just a couple switches by using some masking tape to represent the track as you work around the room. Photo attached of how I do this. Then I KNOW the track will fit as I planned. No matter how carefully I draw my sketches, the track doesn't fit the way I thought it would. Obviously, using trackplanning software would rectify this, but I'm a little old to learn too many new tricks.
I based my planning on a prototype railroad. This kept me focused on what specific industries to include, as well as the scenery of the area. Since you know the geographic area you are interested in, I would suggest making some notes on the railroads, the industries they serve, etc. That might help you to decide if you want to use two or three really large industries, or several smaller ones.

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