Firstly, congrats on finding your back to Linux even after having to relearn everything from scratch! People often rhetorically ask, "given another opportunity, would I do it again?" Now you can say, yes! :⁠-⁠)

About your installation issue, all Fedora media has a check media option in the boot menu. Next time, use that to be certain and avoid wasting any time :⁠-⁠)

About installing multiple desktops, "heavy" really doesn't matter as long as you have disk space. I hope you upgraded the internal drive to a nice 1TB SSD, they are pretty cheap these days.

That said, since nowadays a desktop also provides certain services, sometimes having multiple desktops can clash on these services. I've found this to be the case if you install 2 "big" desktops, like Gnome & KDE, as opposed to, one "big" and other lightweight desktops. Often the desktops have a way around by enabling compatibility options. This is because often users might prefer one desktop, but want to use a major application from the other ecosystem. You have to find out about these compatibility options.

Unfortunately I can't help, I use XFCE, of course on Fedora!

PS: do checkout the flatpak options as well, specially if you have to use something proprietary. They are much better supported on non-Ubuntu systems.