you have mods that can move blocks right?
well if you just treat each sphere as a point mass, and calculate its direction and speed every time (and store those)
then every step you move every single sphere to its new location and voila simulated orbits.
Act first, then think, then try to find a way to cover up the horrible mess you made.
Si Hoc Legere Scis Nimium Eruditionis Habes