First, as said earlier, I kinda think you should keep cha to saves. Making it harder to dip isn't a bad idea, though, so around 5-7th level could be nice.

Second, the mount is far too much a concept thing than a class thing : imo it shouldn't be the only option for the paly. Maybe using PF divine bound? Furthermore, your mount has no written progression above 14th level. Is that intended? It's at those levels that something like a mount will die really easily. If you're looking for mount features, adding the template half-celestial could do a lot for it (and make it far more intelligent than our poor paly-boy, but we usually don't care...).

Lastly (I think) if you make casting Cha based... why not making it spontaneous with access to whole paly list? I mean, paly should be easy to play, and having to choose few spells in a very short list can just make that daily list full of mistakes. That would mean more slots per level, too, and keeping in mind that the paly won't skyrocket his cha as high as a primary caster he'll need it to do more than just casting one spell once.
The idea behind domain casting is nice, but... why not giving them access to casting all domains from their god/source?