order some professionally cut, measured and prepared benchwork.
So I braved the cold weather in the garage and started to go through the box. The box was smaller than I would have expected for all the materials and space this layout would ultimately take up, but it was quite heavy nonetheless - and it took a beating in transit as well, with one of the two outside corner curve sections having gotten cracked (I've contacted the supplier about this today to see if it can be replaced).
ModelRailroadBenchwork's website, are much better than anything that I could (or want!) to put together on my own! These are solid 3/4" wide sections of plywood with all the screw holes, access holes, and bolt holes already pre-drilled.
So far, I would have to say that if you can afford it (my total cost for all of the above, including shipping, was $460, plus $96 to have it shipped from Florida to Washington State) and want a sturdy benchwork and cannot do it yourself at any decent level of skill, this seems like a decent option!