Forrest, your layout looks mighty nice. And as you indicated, you had a bunch of criteria to include and are happy with the results. That's VERY important.
For anyone "starting" to plan a new layout, I'd definitely write down a list of things that are important to them. Then prioritize wants/desires in the list. Don't rush to run out and purchase and cut lumber! Make a few track plans... maybe even post them here on the forum to get feedback from others -- whether the layout is big or small.
I've seen absolutely FABULOUS O-Gauge layouts created in relatively small spaces. Lots of layout techniques can be used to "compress" the action into smaller real estate footprints than you'd ever first imagine. Look at some of the stuff posted online by layout designers -- TrainWorx is one great example. Dunham Studios is another. These companies have done large and small layouts in a wide variety of designs... and they all look superb!!! There are some great layout-building and scenery techniques that make this all possible. (It's no small irony that some of the great custom layout builders have also spent time with Broadway set design/construction!!!)
Certainly a lot of considerations go into a layout design. Some folks want to run LOTS of trains simultaneously. Others are happy to have a single-track mainline with a broad variety of industries packed into their railroad real estate to accommodate realistic railroad "operating sessions". Lots of factors to consider.
But yes... if running articulated steam locomotives, full scale-length 80' passenger cars, and the likes of 89' auto carriers all rank HIGH on your list of "must have criteria", then we're talking lots of real estate to support curves where these monsters look "at home".
Don't take this the wrong way... but I've pretty much come to the conclusion that even O-72 doesn't cut it for the larger full-scale products that the importers are giving us these days. My initial space that I had planned for a hi-rail layout ended up going towards a MUCH different Standard Gauge layout (approx. 10' x 28' island design), once my O-Gauge interests trended toward the larger full-scale rolling stock. I now have two layout designs I'm considering for the "grand" O-Gauge layout -- one I posted some time ago here on the forum, and an alternate slightly smaller design. Yes, reality always seems to rear its ugly head even when we have the luxury of starting from scratch!!! But whichever option wins out in the end, I hope to be happy with the result, 'cause I'm attempting to factor in LOTS of design elements and feedback BEFORE cutting the first piece of lumber.
David
P.S. Oops!!! Forgot to mention that with my two new O-Gauge layout designs, they both feature a double-track mainline with O-99 and O-108 curves minimum... and the larger design has several areas with extremely broad-sweeping curves for great visual effect -- especially when running passenger trains containing 10-12 full-scale-length (21") cars, like the Atlas-O California Zephyr or some GGD consists. The larger articulated steamers should look right at home on those sections of the layout as well.