Frog God's Fane is Complete Scoundrel, right?
On hearing it, it does not exactly sound like I'm gonna get it past my DM, but I'll try.
Concerning the idea of going Prestige Paladin:
I'm not sure about that. The concept I have now kinda puts emphasis on my character not being a strong melee combatant and I don't want to change that now, one reason being that the thing our group does not lack are, in fact, tanky melee characters. I'd rather be some sort of divine god, really.
Moreover, going two levels would be at the cost of one spell level. But it would give me divine grace... oh well.
Let me go into some detail on why I thought about getting a mount. One of the points is, obviously mobility. But then I could buy a horse, after all. Second point is: It's way better if it offers me the possibility to fly. Third point, to me most important right now: as it's the Shackled City, it has to be able to follow me into dungeons and still be useful there.
Fact is, it would improve my survivability greatly if I was able to escape my opponents easier that way. Even if it really only helps on the first levels it's good, because I get stronger and a lot less squishy the more turning attempts i can acquire.