for number 4, I use the tree-style-tabs addon and some custom userchrome css to get that and it works great. I have it set so that when you hover over the 4-pixel wide sliver that I leave visible (could make it transparent, I just appreciate the reminder that it’s there), it pops out to be 260 pixels wide. I wish it wouldn’t need that level of customization, but it does work.
I actually don’t use the “tree” part of it at all. I don’t get it either. It just happens to be easier to wrangle into what I want than other options like sideberry.