My first addons 6 years ago were DamageMeters but since its and old addon not working any more I suggest using
Recount.
Later I added
Omen Threat Meter its still working but since its too much info for me right now I woud use
BasicThreatBar.
If you are at max level
BigWigs Bossmods is a nice addon if you want to raid.
I think this 3 are easy addons that provide extra options to Blizzards interface and they will not replace any of Blizzards options. Everyone shoud have them
I don't agree with Magicalhats27 the 3 addons you suggested are addons I woud recommend for more experienced players. I personaly did not even use Nameplates my first year of wow and I did not level up any profession because it was just to much for me and not fun so why Gatherer?
Also I was realy comfortable with the normal bags for a long time.