I know for a fact that you could. That is how and when I got started in WoW. I can not provided proof or dates however. You ar eon your own there.
I don't really know offial worlds first things as I'm horrible with dates but somethings include:
First F2P DK
First sea turtle
First GoC (lofi and friends?)
First FtA (kale?)
First US bloodthirsty (coming soon)
First rivendares (felix?)
First precious ribbon (that Chinese guy? championa or something like that)
First person to 3k achievements pre MoP (kale I think or thor I think)
First person to 4k achievements post MoP (Believe it was felix)
First person to 5k acheivements (no1)
First person to get tabard of the explorer
First The hallowed F2P (IAT?)
Like I said those are just some ideas I can think of. Some of them may have threads linking who the person was and some may not. I honestly have no idea and don't plan on finding out GL if you research these
What is MVP? If it's something nice, then thanks
Speaking of the 24 slot bag, how would you know you got it first? Not everyone comes to this site every time they make a discovery, or perhaps they speak a different language. There's no achievement for getting it either.
Just after Kyle posted it, I took my ass to grind it, took 3h. There is high chance that I actually was world 1st f2p with it, but I think I have to delete it from my sig - I think "showing off" at something so low is simply being asshole, as I could spam my sig with "world 1st f2p (put any stupid thing here)"