Workshop / Shed materials help

A few bricks would give you a bit of lift. It's good to have a bit of air circulating underneath too as it helps keeps the damp down.
Looking good.

 

Think i would have raised it slightly to allow air to move around underneath easily.

 

You should be able to lift the walls and slide the floor in underneath.

 

I'll second that, you definitely need to get some air underneath, for a small amount of time, you will save a lot of hassle later.

 

You could cover the exterior walls with charred wood cladding. It`s a longevity method and weatherproof: it has been used in Japan for a long time where climate conditions range from semi-tropical to northern. You can find it here: https://degmeda.eu/