15> Calculating near is a pain in the ass to calculate, for every unit. You'd have to calculate every units nearness to one another, using a fp (slow) calculation, to create the list of relative nearness, then sort that list.
33> Actually, the first organized use of horses in war, were based on Chariots, since they didn't have viable saddles yet. These chariots would have likely been 2 horse teams, with a moderately small, 2-wheel chariot... thats been confirmed through archeological research, and testing. Appropriate styrups, and bow techs allowed horse-borne archers. Use of other weaponry from horseback, didn't happen til much later.
34> You can assume that movement is abstracted, in any civ game. Roads also abstract appropriate vehicles for the units on them.