I wish you the best of luck. In my Seducer shape shifting mod for Oblivion, the most complicating issues were related to faction management. The shape a player takes (if you're planning on implementing changing into other player races as well) requires some interesting hurdles to be overcome when it comes to how a faction responds to the player, since this will depend on the current shape the player has. Added to this, there is normally a "limit" on the number of things that can increase the player's standing with a given faction, so you have to be careful how you allow the player to interact with the factions. And if the player is in beast form, all "crimes" committed while in that form must be "forgotten" when the player changes back to their normal shape... unless someone witnesses them changing... fun indeed : ) Hopefully someone will get "flying" implemented in Skyrim relatively quickly, since this was possible in Oblivion, although collision detection while flying was the most annoying part. This will probably require that the Skyrim Script Extender is well underway though before this will be possible.