I bought all new because used market around me isn't big enough. I went for Silverstone for the case (both a 4U and a 2U), and Startech for the cabinet. Cabinet is expensive new, but apparently in some places you can get used for cheap.

The 4U case (RM42-502) is for my PC so I have a full size 2080S GPU, an ATX motherboard, but not that many SATA drives, but I know they are selling either mods or other cases in the same form factor. Since temps and noise were a big priority, I went with a Noctua D12L ventirad. Only downside compared to normal case is the cable management that is a bit more tricky imo.

I've been using a Firefox extension instead that has fairly good filters by default, because I kept getting crap results when looking at technical questions (ie. landing on over-simplified examples without details instead of official documentation).

https://addons.mozilla.org/en-US/firefox/addon/ublacklist/

They publish some subscription lists of things blocked that you can chose from: splogs of GitHub/Stack overflow, Pinterest... And then you can add custom blocks directly from your results list (Quora...). It can be a nice point to start with to use their filter even out of the extension imo.