A couple of rules for you to mull over:
Fliers are considered to be 'flying high' until they charge. In the turn following the charge, they are considered to be low enough to attack with ground troops. Otherwise, only missile troops and other fliers can attack them.
Have line of sight to all other units on board except in forests etc. Can use initiative to charge as per usual rules, or if applicable can be given an order to charge any unit in range and not in forests.
Can end move over any terrain if flying high. If pushed back into forests etc, use rules as usual.
We're still debating how to handle gyrocopters, though even as a non-dwarf player I don't mind them straffing my army with impunity. Well, ok I do, but it seems a realistic use for them, and actually makes the damn things useful.
A unit on a hill can shoot over the head of units in front AT TARGETS THAT AREN'T ON
THE HILL. No, this doesn't make missile troops too powerful, and allows for far better
defended positions.
HILL (duh!) OPEN
cannon
\
h'gunners
\
<-----
warriors________ Enemy
In the example above, both cannon and handgunners can shoot at the enemy. Natch, they don't get to stand and shoot if the warriors are charged. Once the enemy is in hand to hand with the warriors, the missile troops can't shoot (as per normal rules)
If the warriors die and the enemy is at the base of the hill or higher, the cannon cannot shoot over the handgunners (below) (but could shoot at a second enemy in the open?)
cannon
\
h'gunners
\
Enemy___________