I upgraded from RH 7.2 to 8.0. When I read the info on upgrade it told me the install program would check to see what I had installed and only upgrade that portion. It took approximately 20 minutes, but I have what most would call a bloated system and an older computer. It did install from all of the disks and give me the package install screen, where it spent 75% of its time. In other words, it showed me the name of every file it installed. From what I read in your first message, you didn't get this.
I don't know that I would have re-formatted everything so quickly, tho. I would have gone down the path you first thought of--find out what result the upgrade gave you.
To answer your first question, simply starting the program would have told you what is running--8.0 is a major change.
There is also a part in the install manual that might interest you. Red Hat takes advantage of Linux's multi-console capability. In consoles 1-4 you will find different information about how the upgrade is proceeding. The manual will tell you what each does. To access these consoles from within X, use Crtl+Alt+function key. For example, console 1 is Crtl-Alt-F1, 2 is Crtl-Alt-F2, etc. I believe you will find that one of these is a log of what happened during the install.
Anyway, you are now up and running with 8.0. Go to the search function and type in Red Hat 8.0. It will give you a list of threads, many of which will cover the challenges of configuring 8.0--getting the sound to work, adding NTFS support and more.