Open the XML for any unit and you'll find something called levelmilestone that looks something like this
<LevelMilestone InternalName="">
<Level>1</Level>
</LevelMilestone>
This essentially determines what stats a unit has at its time of spawn. Trained units have "no stats" which means they get the default stats from CoreUnitStats.xml.
What you want to do is add this
<LevelMilestone InternalName="">
<Level>1</Level>
<UnitStat_Moves>500</UnitStat_Moves>
</LevelMilestone>
This will give the unit 500 moves.
You also mentioned making flying units. For this, in the same unittype, look for this xml
<MovementType>land</MovementType>
and change it to
<MovementType>air</MovementType>
To change the speed on mounted units only, you'd need to change the speed you gain from the mounts. Those can be found in CoreMounts.xml.