LION used a hybrid. One loop is made on two pingpong tables, the other loop used the open gridwork bench from a previous layout, the along the wall part was made as shown here, with more photos on my website.
The Route of the Broadway Lion The Largest Subway Layout in North Dakota.
Here there be cats. LIONS with CAMERAS
Where my shelf-bracketed along-the-wall benchwork meets my steel stud free-standing benchwork, I simply bolt a piece of steel stud to one side of a (flat - goes into a track on the wall) shelf bracket, then mounted the steel 'C-works-like-L' girder to that at the desired height to allow adequate clearance for the cross-joists on the free-standing peninsula.
Other than the attachment, the L-girder structure is Westcott-standard conventional.
Chuck (modeling Central Japan in September, 1964)
If the tops of the center sections are also going to be 2 inch foam, glue on a 1 x 4 on the ends of the foam, even or flush with the top surface. That would leave about 1.5 inches or so below the bottom of the foam. Then you can just screw these two sections together. You may need to add some additional braces from the foam to the 1 x 4 ends on the bottom to help hold them and not rely solely on the butt-glue-joints of the 1 x 4 to the foam.
Elmer.
The above is my opinion, from an active and experienced Model Railroader in N scale and HO since 1961.
(Modeling Freelance, Eastern US, HO scale, in 1962, with NCE DCC for locomotive control and a stand alone LocoNet for block detection and signals.) http://waynes-trains.com/ at home, and N scale at the Club.
I hate to assume but will do it anyway. I'll assume that your dwg represents 12" per square?
I'd do a mix of both, the added cost of lumber should less than the cost of many, many shelf brackets. On the narrow sections I would mount brackets at 24" to 32" centers (depending on your stud spacing AND depending upon the the strength of the brackets) and run 2 pcs of 1x3 lumber on edge parallel with your track on top the brackets. The wider sections and the penisula will definitely need more support as well as both sides of your gate.
If this looks like deja vu all over again - it is... I posted this in another thread concerning trackplan. It's an early 1st draft in N scale - revisions are underway. The general configuration is pretty much a given; the "duckunder" in the SW will probably be a swing gate, lift-up or drop-down.
My question(s) now are more about benchwork. The layout base will be 2" extruded foam. Most of the along-the-wall sections are relatively narrow; I could support them with shelf brackets.
The wider portions and the peninsula will require something else; I'm leaning towards open-grid. Although I pretty much detest building benchwork; it's within my skill set.
How could I do the transition from the shelf sections to those that are grid - or should I just bite the bullet and grid-frame the whole thing?
Is this making any sense at all?
Rick