If was was to go thinner and taller, the only thing holding me back at this moment is the way I decided to mount the brake caliper.
I suppose some sort of “Z” bracket off the back of the frame could remedy this.
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For comparison sake, all MTB or other bicycles equipped with disc brake have the caliper eyelets set parallel to the dropout by default because the caliper itself handles the offset. Offsetting calipers to line up as needed with washers is not uncommon, and mini bikes with disc brake tend to be done exactly the same way. In fact the most have the same exact caliper ISO mount dimensions as an MTB.
A stepped in offset is not an issue if the material thickness and hardness is adequate, however reducing the axle length and spacing to the dropouts is the safer way to go.
Why?
Simple, Physics dictates that regardless of the material in question; the long the span the greater the deflection, even at rest.
A simple example of this is a 10ft 2x4 compared to a 5ft. The five footer will have nearly no flex on its wider face, where the 10 footer will be very springy.
This is why "Freehubs" took over in high quality bicycle components leaving freewheels for cheap bikes.
A freehub has less overlock, but more importantly the bearings are as far outboard as mechanically possible without interfering with the cog lock ring therefore maximum support.
I digress
The point being the span (more specifically unsupported span) and physics involved; instead of moving the caliper to the rotor, move the rotor to the caliper by using the least amount of spacing you can mechanically get away with
