The green column looks like it was designed with space for a full 6 spots but 4 are removed nerfing its use. 2 slots is not enough. I want to be able to cycle through pickaxe, axe, shovel, shears, machete, hose, empty bucket, silk touch tools, torches, et cetera.

too op. tools is enough.
hose won't work as it uses the same shift-scroll function to change modes.
no torches as it only works with un-stackable items and its not necessary.

you should add this mod on top. they work well together and it will hold the hose and any non stackables e.g. hoe, sword, silentgear slingshot & so on
Tool Belt

you can upgrade it too. more slots, i have 7 slots and the backpack on top. works great :)