...which is a shame, really. Mounted archery isn't easy to pull off effectively.
As for Crossbow Sniper, you really can ignore the increase to your sneak attack range (30' -> 60') and it's still a decent feat. The feat that gives full Dex to damage on any ranged attack is just... uneeded. I would say even somewhat overpowered. Archers don't need more loving in this game, except for perhaps crossbow archers.
Now, I would think that one very good question would be this: why do you want to be a mounted archer?
The benefits in the game are minimal at best, unless you plan to fight your battles on relatively HUGE battlefields (in D&D terms), as a mass of troops against other masses of troops. Then the ability to race around the battlefield and apply ranged firepower to the enemy nearly at will is a proven battle winner.
Or perhaps you plan to hunt dragons, or other flying creatures prone to retreating when the odds are against them?
Otherwise, seriously, you're better off on foot, on a flying mount with a bow, or mounted with a lance for charges.