No, that definitely would not have ticked me off, especially enough to write a letter. Mountain out of a molehill? Well, yeah... IMHO. These things are pretty common in hotels inside and outside of Disney, so always remember to put the Do Not Disturb sign out. Then if that happens, you have a right to complain. As for the housekeeping supervisor knocking and walking in, I am sure that was an honest mistake, and embarrassing for her, as well. She probably won't do that again anytime soon. At least she was being responsible enough to come and check the room to see that everything was in order. The mistake with the ressies could have been with the front desk, or the people on the other end of the phone... so since you at least got seated, I wouldn't give it another thought.
Letter writing should be saved for REALLY catastrophic things, not inconveniences. As I said before...it's only my opinion.