JC, yep, to sum it up, that's what you do. If you know your going to build the Fall Creek, than build the 15" x 12' bench work, gather the pieces you need to get started, and start making the plan fit your space. If you don't have a 12' long space, make it an "L" shaped plan, use 26" radius to make the bend. And like IronRooster says about the turnouts, use the #5, that the plan called for. Once you get started, it will all become easier. Don't overthink this, just build your space, get some track and switches, and start laying it out.
If your afraid of flex track, you can buy sectional radius that you can make work. But there is nothing to be afraid of with the flex track. Just start working with it, and see what the "flexibility" of it is all about when it comes to locating curves, switches, etc.
The only way your going to get a plan that lays it all out for you, is to go back to Cuyama's post at the beginning, and buy a planning book, put out by a track manufacturer like Atlas and Kato, that gives you a list of materials, and follow along.
Build your bench work, get some track and switches, and jump in! You'll love it ! Don't let it intimidate you.