Have you tried rust removal by chelation? Might save some of the coarser sanding? Good pictures in the "restoring old vises" section. Build a bunch of wooden drawers to surround and separate those toolboxes. Makes the mismatch look intentional.
https://www.evapo-rust.com
The wood shelves catch and hold dust. Leaf blower works. Might use ventilated shelves or add skirt or doors. There is a post here where a guy did that and it looks awesome.
Are there any specific rules against movable storage? I have an acquaintance who purpose built a cargo trailer and moves it around the yard every spring. Might build the 10 x 8 first. Then the cargo trailer. A brown job box will take a lot of weather and is pretty low profile. Build a deck with removable floor panels to cover. Cover three of them with cushions and call it a cabana. How tall a 10 x 8 can be built? Are tree houses allowed? Store stuff there and relive your childhood. Can you build a pool house, playhouse, or outdoor kitchen that is actually storage? Mother in law apartment? Artist studio?
Is your HOA builder owned? Elected? Professionally managed? There are many posts about how to manage or at least cope with each on the internet.