Regarding 4; I suppose you’re looking for the ArcMenu extension if you wish to continue using GNOME as your Desktop Environment (will be abbreviated to DE from here on). Though GNOME’s workflow is considerably different to Windows’. Therefore, you might be interested into looking elsewhere unless you’re actually interested to continue GNOME. FWIW, GNOME is one of the most popular and most polished DEs out there, but it’s very opinionated; which rub some folk the wrong way. I personally like it, but others might differ on this. Lastly, GNOME is NOT particularly known to be light. Therefore, if you’re not happy with how it runs; e.g. frame skips with animations or just high RAM usage overall, then perhaps consider Xfce or Lxqt. If you’re not discontent about the performance on GNOME, then you could also consider KDE or Cinnamon as those might ‘feel’ more ‘modern’ than the aforementioned Xfce and Lxqt.
Regarding 5; Ubuntu gets a lot of hate due to:
how they’re forcing Snaps (their in-house universal package manager; therefore a direct competitor to Flatpak) onto its users. So much so that even attempting to install some packages through apt will result in the Snap being installed instead; which is basically unprecedented within the Linux landscape.
some mishaps in the past resulted in very bad PR; especially to those that are privacy-conscious and/or F(L)OSS-advocates.
You’d have to get to your own conclusions though. It’s probably still the most used distro and therefore you might expect some QoL-features are only found within. If you’re inconclusive, just try it out and consider reporting back to us on how it went. Regarding old hardware; the DE is the most important factor anyways.