I chose an around-the-wall plan. However I decided to make the basic shelf extension 3' deep from the wall...my farthest comfortable reach. I have 3 support posts in the basement holding up the main steel beam for the first floor. I built each post into the end of a peninsula. The peninsula walls, no higher than the layout height and fastened to the concrete floor, also have a 3' cantilevered shelf on each side.
That said, my basic cantilever support structure (standardized for quick assembly) has a 45-degree brace to the wall in each bracket. Brackets are about 4-5' apart. That's plenty sturdy for the layout.
But a while back I decided that as I work on the layout, particularly if I'm leaning hard on the outer frame rail, a portable leg would be a good idea to give extra support when needed. So I made one...out of a length of PVC pipe, notched at the top to engage the 1X4 frame rail and fascia, and having a cap on the bottom into which is run a carriage bolt with a rubber pad on the head. Ergo, I simply slip the leg onto the rail/fascia, hold it vertical, and manually spin the carriage bolt out until it contacts the floor and sits snugly in place. When done, a few turns of the bolt and the leg comes free, restoring the clean cantilevered appearance/functionality.
We also purchased inexpensive stackable 4-layer plastic shelving which with a few simple pieces of 2X4 and plywood scraps and eight casters, convert to two 2-shelf roll-arounds for under-table storage of...what else?...wretched, embarrassing excess, of course. Waaaay too many of them, though!
Anyhow, the portable leg has been an excellent alternative from my experience. I try not to over-build...or under-build, for that matter!
But, as always, TEHO.
FWIW,
KD