firstly there are no 'celestial bodies'. there is no space. everything up in the sky is just pictures that illuminate the world underneath - this is provably true and conforms to the multiple spotlight model'. One could follow the sun at breakneck speeds, but it would not affect the length of day in any way. This means that each minecraft person has their own individual sun/moon-spotlight that follows them.

observably you can never reach the edge of the world cube. the world is a seemingly endless flat plane.

round

ender pearl, eggs, buckets, etc