According to the Pathfinder wiki, he used to have the Liberation domain in early texts, but apparently someone realized that meant he had 6 domains so it was removed. It is kind of strange, really, since it means that the only god in the Inner Sea pantheon with Liberation is Desna, while all of CC's other domains are shared with at least two other deities. Personally, I'd have dumped the Charm or Travel domain (probably Travel, so that he didn't share 4 out of 5 domains with Desna).
Come to think of it, the description of his herald, Thais, in Inner Sea Gods says that he used to have 6 wings, but one got chopped off by Asmodeus. Maybe this is a reference to that?
There are ways the GM could work around this, both by the rules and by stretching them a little. In the end, however, make sure your GM knows exactly what he's getting into with this (maybe show him this thread?) and abide by his decision if he thinks it would create too much hassle for the other players.
I've never played this AP, but there is actually an escape clause in the Oath options stating that you can give up the oath and return to being a regular Paladin under certain circumstances. Namely, if you make the oath for a specific act (e.g. killing a particular demon or something) doing that action discharges the oath. Maybe your GM could suggest a particular goal for your oath so that you get some good roleplaying out of it early on but can get free from it before things become really sticky?
Paladins who take up an oath may make a sacred promise to their god or temple to perform some specific and grand action associated with the oath. For example, an oathbound paladin who takes the Oath of Vengeance may be tasked with killing the orc warlord who razed her home city, while a paladin with the Oath against the Wyrm may be asked to secure a nonaggression pact with a family of dragons. When a paladin completes the sacred promise, the oath is fulfilled, and she may abandon the oath if she so chooses; she may then select another oath or become a standard paladin or a different paladin archetype.
I think the Adroit ability can only apply to skill checks, not attack rolls, but otherwise this looks rather terrifying!
Adroit: Choose a single skill that can be augmented by the item's legendary surge. As a swift action, the item's bonded creature can expend one use of legendary power to gain a +20 insight bonus on the next check she attempts with that skill before the end of her turn. The item must have a legendary surge that augments skill checks to have this ability.
Interestingly, the Player's Guide to WotR explicitly states that Tieflings are not unknown in the Crusade nowadays, so the info in Blood of Fiends may refer to an older time (or someone just retconned it a bit for the AP). Either way, Tieflings are explicitly.
WotR Player's Guide wrote:
Races: Outnumbered and facing an assault from evil outsiders, the crusade today has no compunctions regarding race when it comes to outfitting its forces. Able-bodied men and women from all races are welcome so long as they are willing to fight the good fight. At one time tieflings were distrusted and shunned, but now some of the fiend-blooded fight alongside aasimars while defending Mendev or striking against the horrors of the Worldwound. Many tiefling crusaders claim that their blood makes them the best suited to fighting demons, and they also have defenses that help them shrug off some of the demons’ deadliest attacks.