In my similar space, the thought process was "how much surface can I fit in here, without a duckunder, while allowing for display shelves?". Several years later, I still don't know if that was the correct approach, and folks have offered a lot of good insight in the preceding posts.
I built a table that can be walked around (2-3' clearance to the walls), and then I built shelves along the walls. In hindsight, it might have been better to go around the walls. However, had I done so, it would have been difficult to create accessible storage for the items that aren't on the track. So I guess that one question to ask yourself is how much stuff do you have that won't fit on the layout, and how easily do you want to be able to get to it. One can build shelves along the front of the benchwork, but doing so exposes the shelved items to knees, feet, and curious children.
As for indecisiveness, I'm a member of that club. My advice on that is to build benchwork that you think will work (use screws, no glue), lay some track (don't ballast it), run it for awhile, and see if you like it. Chances are that you won't like some or all of it - so remove the track, reconfigure the benchwork, and try again. If you go with L-girder benchwork, it's easy to make areas larger or smaller.
At your club, make notes about what you like and what you don't (the layout, not the people!) and apply that information to your planning.
Don't feel like it has to be perfect the first time, and don't be afraid to change direction on something that isn't working.
