Mounted have longer movement rate, but cannot go upstairs. They are unable to pick any treasure. Also no option for dismounting. Stat wise they could have thug and knight stats with point higher fight (easier to fight from horseback) and one point less in will (have to control horse).
No other special skil rules. +1 to hit them is not needed - mounted models are higher so usually cannot get cover.
I agree with all of this, except I would also give them Large (which would give a bonus to hit them with shooting attacks).