And regarding backpacks.
I know a perfect backpack doesn't exist until you try Remote Equipment : D
(just kidding)

Overall specs/gist of the Remote Equipment Charlie 25, might get you interested
Reminds of a mystery ranch, that your friend has, but with improvements

- Has implemented your idea with your custom backpack shelves, but vertically, might work well with your 3-tier-item-system. Just to have 3 groups of items, at least.

- Weights as Minaal Daily or lower, if you take out frame sheet. Weight per volume is much better, but don't have numbers at hand, smth around 50%.

- Made out of ECOPAK fabric, that is actually waterproof (compared to minaal)

- Size goes from 15L to 30L (you don't need that space, yes, but more tea to bring back, why not).
- Removable frame sheet to get it under 800 grams

- To me personally much more comfortable due to load-lifters and some harness tapering magic, than minaal, might not be the case for you


Upon the first look, please, try to look past the marketing materials. They don't emphasise how slim it can be in reality, that it has actually 3 dividers inside and that it's one of the most lightest backpacks out there.
They show off more "pack to the brim" marketing materials.