Here are my initial thoughts, Jeff -- and to start with the big disclaimer that there are many people here with a lot more expertise. But I've been thinking about this stuff for three decades, so I hope I have something to offer.
1) If you haven't already, give "track plans for realistic operation" a read-through. A lot of the specific plans in that book do tend toward the "bowl of spaghetti" look although they are very thoughtfully constructed. But the principles in the book are timeless.
2) Chief among those principles, to my thinking, as Armstrong's prescription of weighing your "givens and druthers" -- which you're already doing informally.
For instance--Givens:
I have a space that is 10 feet long and 6 feet wide. It is a corner space of a square workshop, so some sort of L shaped benchwork would seem to make sense. I don’t want to attach anything to the walls,so something free standing is in order. I could build it on wheels for complete access to the back for scenery building if need be.
Druthers:
Being absolutely historically correct is notessential. I would like double main linesto run a passenger train and a freight train at the same time. Diesel engines. Modeling something similar to the SouthDakota Black Hills/Deadwood area so I can do some mountains, bridges, tunnelsand the like. The freight line wouldserve a mining operation.
While not super into switching operations, I would like asmall switch yard and, as mentioned above, a spur for a mining operation. I also plan a small town with a train stationfor the trains to run through. As manyheight changes as I can comfortably have and the longest runs I can have would be great. DCC of course.
3) For more ideas go and buy "101 Model RR Track Plans" by Linn Westcott and "101 more Model RR Track plans" by Jeff Wilson.
Also, get a hold of a special issue MR put out about 4 years ago on "102 Realistic Track plans."
You will not find a perfect plan in any of these. But the more you see, the more ideas you can get about what appeals to you. These 3 books have a wide variety of ideas and arrangements. Another one is coming out this month from MR: , "103 Realistic track plans" and I suspect it will also have some.
I've already *finally* settled on my plan, but I can't stop looking at and thinking about other plan ideas. Not that I'm going to build them, but I just find this aspect of the hobby especially fascinating.
Also, a Model Railroader mag subscription gives you access to the magazine's growing online database of track plans, all of them downloadable PDFs.
4) You do not need to attach to the walls, but I'd suggest you go for a walk-in or similar design with some of the layout against those corner walls, instead of an Island approach, with areas no more than 2 feet deep unless they are accessible from both sides.
5) I've always thought a really good general schematic for people who like to mix big main lines and small branch line operations in a relatively small space is to use one portion of the layout to model a snippet of a main line through a major stop (that also gives you your switching yard and your station). The rest of that main can be fairly simple (and much of it hidden) and complete a full circuit. That way you get to see trains run when that appeals to you. Then your mining branch occupies the other portion of the layout (and probably goes over some of that hidden main line). I still have a copy of the April 1970 MR that has that sort of plan and that I think could be a very successful design. (Just doesn't happen to be my particular taste.) And it's just one of very, very many.
Now I'll shut up and let those with a lot more experience -- not just decades of theory

-- chime in.
And welcome!!!