The growth has been purely organic. I cannot say any of it is really planned ahead of time. I use 16U vertical rails for each rack, and then build a cabinet around them that works for the space it is in, e.g. 32U in the cat bathroom rack, which is 16U side-by-side with another 16U. The arcade cabinet rack is 16U technically, but I only have 6U of rails in there, as the other space is pull out drawers to make it easier to work on the workstations without having to deal with cabling issues. 16U at the RV.

For permanent infra, I tend to buy new, because I want that extended warranty and am not interested in buying somebody elses problem. For projects, it is a mix of ebay finds and road-side or ewaste center salvage. I don't watch TV, but I probably own more 55" 4K TVs than any one person I know, because I salvage them (people in big cities throw out all sorts of stuff with minor electrical faults) and then turn them into personal projects, e.g. a touchscreen cat toy, a waterfall ring toss game in the door of an art gallery, a virtual window.

Some days it feels like everything is held together with string and chewing gum.