Yeah, it's like normal combat, but there are a few things to consider:
1. You can't "Dash", if anything, your mount could do it as you are using its movement. Whether you can bring your mount to do it I'd make it depend on how familiar the PC is with the mount (usually not familiar enough). Obviously that also means a rogue can't benefit from Dash as bonus action.
2. Making an enemy immobile or knocked prone makes him fall. (I do allow a single turn in before someone hits the ground. Max falling damage is 20d6.)
3. Don't even try to track positions. It's a nightmare in 3D. Just define the distance instead.
4. As DM you have the power and I think it's quite reasonable to give disadvantage on melee attacks, but that's really up to the DM.