Doughless
I've built 2 layouts using only a power chop/mitre saw to cut the x3 or x4 sticks. I let Home Depot cut the plywood. Yes, the layout ends up having square shelfs but that just leaves more room for scenery than carving out a different shape.
If I wanted the plywood to curve in places I assume the only tool to use would be a jigsaw.
For sure the big 4x8 sheets are easiest to have cut down at Home Depot or Lowes etc. such as the large flat yard areas:

Heck, even if I had a table saw, I can't get the 4x8 sheets home since neither car will fit them. But I can fit in a 30" x 8 foot sheet.
A mitre saw would definitely speed things up vs a sabre/jigsaw. The down side to a mitersaw only without the jigsaw is cutting the sub roadbed curved pieces such as in the photo:

Conversely, a jig saw will let you cut the 3x and 4x frame pieces as well as the curved pieces, which is why I was able to build this layout with only the drill and saber saw.
As for assembly, I use a hammer, finish nails, and yellow glue as well as a power screw driver/drill.
Nails will work of course, but drywall screws are great because it was a snap to disassemble the layout down to bare benchwork components when it came time to break it down and move.
I simply backed out the screws and took things apart and saved everything including the screws.
