In case you guys are still looking for Light Cavalry for the US, you could use the Boston Hussars. They've got pretty... unique uniforms, to say the least.
Also, the 6th Innskilling had a detachment in the War, so having them act as heavy cavalry for Britain would be a nice balance. You could also add the Quebec Light Dragoons, as I don't thing they were given muskets in the early stages of the war so they could probably be used as Britian's light horse. Either them or Dorchester.
But hey, y'all are almost done. This stuff could be saved for a second release.