hi Real,
small? better go for: not to complicated or not to big. You could make a great start by drawing your room.In 102 Realistic Track plans published by our host you will find how to do it properly. A book worth its money anyhow and you can bring, if you like to do so, the drawing in to this forum.
RealSturat:Past that I was thinking perhaps a simple around the walls layout 9 x 11 size, but the surface area would not be much more that the 4 x 8.
If I understand you well, you mean that you can build a 9x11 sized pike and that the resulting train space is about the same as on a 8x4; you hit the nail on the head.

A sheet of 5x9 is cut into pieces and rearanged into an other footprint. Both need the same space; train- and manspace are flipped.
But the resulting pike can accomodate so much larger radii, has so much more length and... and..... The result is a shelf-layout along the walls. Ian Rice wrote a book about these layouts, and Lance Minheim not only wrote such a book too, but called his design and building entreprise "The Shelf Layout Company". Need I say more? You inherited some big engines and and coaches, they will love those bigger radii and that longer mainline. That 9x11 is a great start!!!!

The Hog is a beginners layout, wel covered on the internet, to show what can be done with one sheet of a 4x8 piece of plywood. It fills a 9x9 space.
BTW when you apply a layer of plywood you do not necessarily need foam and when you use foam you do necessarily need a plywood layer under it.
TMHO most people chose to build a 8x4 because they think it is easy. In reality it is just as complicated as any other kind of build and is resulting most of the time in a bad trackplan only.
In the very same 102 trackplans these issues are covered too. The famous book Trackplanning for Realistic Operation by the late John Armstrong covers these issues in depth. The first edition was written 50 yrs ago, but newer editions are updated and worth every penny. The book has chapters on the prototype, on setting standards to get reliable operation, on technical backgrounds (overhang, switch numbers, etc) and on how to apply those when designing your own pike.
A far more complicated switching design that fits your space, designed for the Omaha Road Man.

The tracks to the very left, that seem to go under the Fire Stone plant, are supposed to be an interchange with "the rest of the world", so called staging. A lot can be done in your space.
Keep smiling, have fun
Paul