Ok, lets answer some of these questions since the answers are already out there but people seem confused. Ill go in the order I found them.
Do you still need to buy WOTLK to play deathknights?
Yes. Just like with the monk, you must have the WOTLK expansion to play the DK class that came out with that expansion. They are only unlocking the races, not the classes.
But can you preorder a race change?
Like purchase a race change now and on sept 25th, change into a pandaren?
No. Preordering a race has never been a feature, and is unlikely to begin being a feature.
This part aside, does this mean a person could make a Pandaren of another class ready to play as of September 25th?
No. No one can make a Pandaren of anything until the expansion has launched.
Can you apply grantable levels to a new Monk in MoP?
So for instance my RaF friend leveled two characters that granted me 80 grantable levels, can apply all those 80 levels to a new Monk?
RaF works with the new Pandaren races. A blue already stated this. That would make it safe to assume all features would be able to be usable on a Pandaren or monk.
Zarhym, then, do the starter editions also get to play any race?
Everyone, despite what expansion they have, will be able to use Every Race. They are removing the expansion restrictions from the races. Not the classes.