With the cost of lumber and wood up 300% just in the last 100 days, you might want to be gentle with what you remove.
With my build, weight watching was the number one initial concern. My walls were 3/8" Dri-Deck material.... or whatever they are calling that new wood product they use on the floor. It looked and smelled the very same as the floor, only thinner.
The thing was, it was WAY HEAVIER than I wanted. Having built many, many van, trailer and truck interiors over my lifetime, I set out to find my favorite wall material.. what they used to call LUAN. I had to travel to find it as most places no longer carry it. Their replacement.. 1/4" "Plywood" is heavier and less flexible than actual Luan which tends to have a softer core than traditional plywoods. I did take a square foot of both materials and weighed them... But I think I wrote their weights on the squares and not sure where I put them ! Considerably lighter though.
1/4" Luan (4-6mm) is plenty for sidewalls as long as you fully work out where you will be hanging any heavier things in the interior down the road.
What you already have though with your load capacity is probably just fine. In my case, I upholster the walls, a thin layer of foam, then cloth or vinyl to suit artistic design goals. I'm not a fan of just a cold painted (or aluminum skinned) interior that echos like a cave. The foam can be as minimal as 1/8 to 1/4, which under a textile adds insulation and noise control while looking great.
