William Bronson

Neat experiments!
I suspect you could cut either the lime or the plaster of Paris with something neutral and white, and get food results.

Plaster of paris is kind of expensive to me and I've always gotten good results with  the 30,60 and 90 minute dry wall mud  that comes dry and is mixed onsite.
Very predictable working times, and drys plenty hard.

Will your final project be over unstretched burlap or something else?
That will effect durability.

I  have 20 of them, probably more.
I store everything in them, both indoors and out.
Tools, food, canning goods.
I have a kitchen island made up of 3 of them side by side.

I have played with using them for wood stoves.
Lots of people use them for smokers, but I can't get past the toxic ick of the paint.

I've seen a worm farm/vermoponic reactor built into one, each drawer holding worms, food scraps and bedding, with water circulating the nutrients through.

I use them to support work benches, or individual tools like a drill press or bandsaw.
I add casters to them.

I've added bike wheels to the sides to create a rolling tool box.

I've used them to raise a bunch of 1/2 barrels up to working height.

They are definitely strong enough to build a shed out of, even the cheapest ones will support more than 250lbs of human.

I some times screw one two drawer cabinet on top of the other, using self tappers.
Pole barn screws work great to secure wood to the metal.

A piece of plywood screwed to the top as a roof will keep most of the rain out, but adding a drip edge will help.
A standard sized commercial baking sheet comes with its own drip edge.

I have laid one on its back, sans drawers ,and poured a slab into it.
By repeating this 5 more times, you can have a concrete lined box.
Screws and stainless steel wire can be included in the slab, to tie the concrete to the metal walls.
This is one way of lining the cabinet to keep paint away from plant roots.
Plastic is more common.

With proper sizing, these cabinets can hold a batch box rocket mass heater core.
I've cast a core in one before, it's crumbling junk now, but I would try it again.
Next time I will build the rmh core from firebrick splits and back fill with sawdust cob.
The steel surrounding the concrete can offer a place to attach a stove door to.
I will try a hotel pan for the roof of the firebox.

Even if you just need a platform to build a rmh on, laying a full sized 4 drawer file cabinet on its side would offer a heat resistant rectangular platform roughly 52"x 25" , 16" off the ground.
You could screw two standard file cabinets on top of that platform and still have space to build a core in between the two.
With or without the drawers removed, metal cabinet heated by the heat from the walls of a rmh core could be very useful.

A 2 drawer cabinet laid on its side creates a platform that is close to 24" x 25".
By using steel studs for framing you might create a box to hold your cob or concrete form, or to hold your firebrick splits.
You might even cast a cob walled bell.

When laid down file cabinets could be used to form the bell of a RMH, in a way similar to the half barrel bench.

I like filling cabinets, a little bit, but in a totally normal way, not weird at all.

Great resource you have there!
I put my most substantial biomass in the base of my beds, and top my beds with the stuff that breaks down easily.

If you have established beds you want to amend, I would use the mower to pulverize the stalks, and top your beds with that material.
I would add some nitrogen to that, alfalfa meal, urine, grass or such.
If you can chip the stalks to chunks, I would use that on top of the pulverized stuff.

There is a version of the pocket rocket stove that is popular in Japanese StoveTube.
Instead of a feed tube, half of the barrel is sealed off from the other with a vertical baffle.
The two sides of the barrel are only open to each other at the bottom of the barrel.
The stoves have a strong,hot,cleanish sideways burn, and a bigger fuel chamber than the standard pocket rocket.

Here a video of one.
It's rather overbuilt in my opinion, but it really shows the design off:
https://youtu.be/RKQSUF8M834?t=502&si=UIRUTEWqkAowR4VZ

If it doesn't need to be portable, you could cover it in thermal mass.

What happens to all the salt when the seaweed is composted?

The Tlud design and burning instructions seem very well done, but I can't find the details on how to use seaweed as feedstock

To prep the seaweed,I would get a 55 gallon drum, perforate the bottom and sides, elevate it for air flow, stick a sheet metal cylinder down the middle,and fill it with seaweed.
After it dried a little, I would pull out middle cylinder
After it dried completely, I would break it up into bits, and use it the same way as coffee husks.

I suspect a controlled pyrolizing of dry material will be safer for human health than uncontrolled decomposition.
I think the compost would have the same problems of being contaminated with heavy metals, but at least some of the other pollutants will be destroyed during the charcoal making process

On a large scale, a seed ball making drum like these might work:
https://youtube.com/playlist?list=PLUQMDg9HfMjhNeUXTlsYEHtce9b3K6qyk&si=rFeisdnR0A6E86