What worked for me on my HO layout and what I plan to do on my 3 rail layout is to simply lay the track in place. I put the main line and passing tracks in place. UNspiked and no wiring. Mark the center line so you can come back and return the track to that place. It would be helpful to also mark the ends of the ties so you know the width. I also put the switches in for industries while marking right of way.
Now my pencil scratching gave me something similar to a trackplan, so now I had to find where the structures would actually fit AND leave room for another industry on the opposite side of the track between the switch and the end of the spur, thus two shippers or receivers on each track...some of the time. If you do not have the structure, it helps to at least know the footprint of that structure. Cut out a piece of cardboard and lay it on the layout top where you want the structure. Make your track go to there and have some "fudge factor" to juggle as needed.
Now simply paint the "non railroad area" with a grass green. If you KNOW where you want roads, go ahead and paint them black or dark gray or even brown for dirt.
You can always paint over the first color of paint should you realize later that the road and structure will not fit in the same area between tracks.
You want more realism? Fine, simply scatter some ground foam and ground cover (appropriate colors for soil and grass, etc) on the WET paint. If you need to add some more, hold it in place with a spray of warm water and matte medium (less "sticky than Elmer's white glue" but stone simple to mix a small amount of matte medium to a spray bottle with water. Shake well...FREQUENTLY. I try to make enough for this project today and then rinse and clean everything after I am done.
I painted hills with a brush and/or latex paint and water mixed in the same spray bottle (which is why I washed it and cleaned it frequently). A "water soluable approach" that I stole from Dave Frary and Bob Hayden's book. It worked so well, I was surprised at my success...you see I do not consider myself "artistic"...and while nothing I did would convince anyone that I WAS artistic, it impressed ME and that is all that counts. No offense, but NO ONE BUT ME is registered to vote in my own EGO elections. (smile)
You get the basics. I would mention that I used a view block down the middle of the table/bench work/shelf so I could get twice the modeling without the visual distraction of someone switching behind me. When I operated that layout, I got lost in the reality of switching specific cars to specific industry spots, pulling cars designated to be picked up and keeping my cars "to be spotted" in proper order.
I am comfortable with painting the Homasote or the top of your layout as a stop gap measure. You can dress it up if you elect to do so.
About the same time I was reading Frary and Hayden's scenery book, I was also reading Allen McClelland's V&O Story where I picked up the concept of Good Enough. That phrase means something different to everyone who runs model trains. While green carpet or layout mat does not make ME feel like it is a realistic scene...the ONLY person who has to be happy is the person who owns that layout.
Once I get to that mystical place (good enough) I know it and stop. Is my work good enough to be in a slick magazine with high quality photography...of course...it can always serve as a bad example.
Just like in the real world, everything has to fit...track, roads, pastures, buildings, industries, yards, hills, ponds and lakes and streams....
My current layout has a Homasote layer on top of all the plywood. The Homasote was painted a flat black color. Over the past few years that paint has been absorbed and oxidized to the point it is a dark gray. The whole idea was a darker background color would help to hide the center rail on my Atlas track. When I am satisfied with my track plan, I will go thru the entire process listed above. But I already know about where everything will go and fit. Then I will fine tune the soil and grass and roads and building plots and ballast for the tracks.
I hope something in the above rambling nonsense helps more than it confuses.