Any comments I make are just my suggestions and my opinions. Others will have different ideas.
First - what are the dimensions of the layout and what material did you use for roadbed? Cork roadbed can be glued down onto extruded pink (or blue) foam with yellow carpenters glue.
I recommend assembling all the track atop the foam temporarily and adjusting it until you have a track plan that is satisfactory. Then mark the track plan onto the foam and begin to glue down cork roadbed section by section, making sure the roadbed is in the exact position beneath the track. I would not glue the track down. Instead, drill holes through some of the wooden ties (between about 9 and 12 inches apart) and use track screws to secure the track onto the cork. I found that Atlas O track screws worked well with the Atlas O track on my layout. This will allow the track to be removed easily if necessary. I would leave ballasting until much later in the layout-building process when you're certain where the structures and scenery will be on the layout.
In my opinion, it is not necessary to ballast the entire track plan. You may be able to omit ballast altogether at the rear of the layout where it is not readily visible. You may also be able to get away just with ballast outside the rails and not between the rails. You can secure the ballast with yellow carpenters glue diluted half-and-half with water and applied with an eye-dropper. This makes things much easier if you ever need to replace a piece of track or disassemble the layout for moving.
Again, just my opinion and my way of doing it.
MELGAR
