Angel Dust's promiscuity makes sense given that he died in the 40s - a time where gays couldn't exactly be open about their attractions, to say the least. Now that he's in Hell, he can indulge in pretty much anything he wants to.
Charlie's Anti Anti Christ behavior makes a little more logical sense when you consider that Satan, who is confirmed to be her father, was once a denizen of Heaven himself. He only sought to Rage Against the Heavens after he was kicked out(although not without good reason), and since Charlie has had no similar experiences with either God or Heaven beforehand, she doesn't have a reason to be jaded or vengeful towards them. Her All-Loving Hero tendencies could easily be the angelic aspects she got from her father shining through.
If Baxter's supposed death aboard the Titanic becomes a canon element, it would explain a lot about his design. First off, if he died aboard the ship, the odds are likely that he drowned, explaining his piscine form. Second, the ruins of the Titanic are confirmed to be 12,000 feet, or 3658 meters, under the sea, which is within the Abyssal Zone of the ocean. No light reaches from that depth, so the animals down their need bioluminescence- explaining why Baxter is an anglerfish.
The easy access to ways to sate vices and indulgence in Hell may be the biggest reason why Hell has an overpopulation problem. The damned souls cannot redeem themselves because they are still indulging in the bad habits and vices that helped send them to Hell in the first place! It's arguably the most insidious part of their damnation.
Alastor's design, voice, and title as the Radio Demon are because in addition to being a remorseless serial killer, he was also a radio host from the 1930s. It makes perfect sense that he would use radio to broadcast his attacks on Hell's elites, and it explains why he refers to TV as "the picture show".
Alastor simply showing up out of the blue one day and obliterating the old guard in Hell for seemingly no reason whatsoever. No one knows how he had the power to overthrow the established lords of Hell, and no one knows why he did it, especially since he doesn't seem to have kept the territory he would've gained from his campaign. The news report on the turf war doesn't mention him even once, so it's obvious he doesn't care about turf. Furthermore, he's managed to survive the annual purges for 80 years, and has maintained his reputation all that time. He's extremely dangerous and unpredictable, and now he's backing the Happy Hotel and no one knows why...