The most famous Stone Castle is the White Tower of London (Tower of London)
yes
The moat is a form of fortification (defensive wall) most people who wish to invade a Castle will need to get across this and since at the time people were quite limited as the type of technology...
It really depends on which type of castle it is, but most castles are at least a few hundred feet tall.
In the actual hamburger, it is pure ground beef. There is never anything added to the meat.