Shou Sugi Ban is a technique of charring exterior timber to make it fairly fire-retardant, rot-proof, and has approximately 100 year lifespan.
While the char on wood does not really insulate due to it not being a carbon foam like the Starlite, if using Starlite externally to prevent fire would work in the short-term; I wouldn't think it would really be durable enough to use as siding and would kinda look like you lived in a giant scab. The wooden siding would probably look more natural and have the grain show through.
With regard to emfs, carbon is mildly conductive so it would likely have a dampening effect if a solid skin was formed, but I don't know if it would be enough on it's own to block EMFs.
With regard to the binder, wheat would probably work, but not as well as elmers as it would be like a dried up dough which would tend to crack and crumble. But it would also probably stink less when fired.
For a natural/waterproof/nontoxic binder and perhaps more durable alternative that could be left uncharred, pine pitch / tar would be a decent place to start. If you need to modify the properties you would need to find specific growing conditions or other plants with the desirable properties for their sap. And I bet that shit would smell amazing when it burned. In order to increase durability having the starlite made into a composite with a fabric (similar to linoleum tile backed with cloth) would be a good idea too.