WMGs for Discworld / Going Postal and Discworld / Making Money. Warning: Potential unmarked spoilers.
Adora Belle is Anoia, the goddess of things stuck in drawers (or possibly could be an avatar or possessed by her).Think about it — Moist has become obsessed with Anoia since the whole praying-for-money incident, said incident increased her worship dramatically, and when Anoia herself shows up in Wintersmith it's exactly the same character as Adora Belle.
Vetinari paid for the Grand Trunk's repairs with the bounty on Reacher Gilt.The Patrician is an Assassins' Guild graduate, he was at least as responsible for Gilt's death as he was for Lord Winder's, and it'd appeal to his sense of symmetry to collect on the Guild contract for that sole purpose.
Vetinari is grooming Moist von Lipwig to be his successor.If Vetinari wants something, he takes one thing to mold it into what he wants. He legalized the Thieves' Guild to regulate crime, then he took Vimes and made him forge a powerful new Watch. For now, the city is not only stable, but growing. In order for it to thrive he needs to revitalize the major public services. So he takes Moist and uses him to resurrect the Post Office, which becomes big business in and of itself. He then targets the banks and the tax office that we know of, planning to use Moist to do so. He would have used Reacher too, if he'd have cooperated. He'd have played the two off of each other to create one ideal successor.
Vetinari is grooming both Moist and Sam Vimes to be his successor(s).In more recent books, Vimes has started to show a streak of Magnificent Bastardry, which he even remarks on in Thud!. Knowing that Vetinari takes a personal interest in his development, it seems quite plausible that this was his intended goal all along. Vimes and Moist represent different elements of what makes his style of government successful. Vimes is focused, has a clear sense of right and wrong, is absolutely incorruptible and has a talent at upsetting established power players, but can be a bit hard-headed. Moist is a born con-man, good at manipulating people and getting them to like him and thinks outside the box all the time, but he's flighty and unreliable unless forced to focus on one task. It's possible that Vetinari either intends to make them compete indirectly to show which one would make a better successor or split up his power between them eventually. Also note how, in his interactions with each of them, he seems to channel the spirit of the other. With Vimes, he's gratuitously obfuscating and manipulative, almost trickster-like, while with Moist, he's a stern authority figure.
If/When Vetinari cops it, Lipwig will be forced into the Patricianship via an assassination contractEven if Vetinari is grooming Moist into the next Patrician, the chances are Moist isn't going to particuarly want the job, because it completely destroys any chance of reverting back to his old life (for one thing, they'd have to put his face on the stamps), and like the other positions Moist has taken, it's not exactly renowned for it's holder's longevity (unless of course you're Vetinari). Vetinari has probably set up a contract stating that he's to be assassinated if he refuses the Patricianship, and Moist will only be informed of this after Vetinari's death. Also has the bonus of stopping the other Guild Heads putting their own person up for the job, because by then it will so obviously have been Vetinari's plan, and nobody wants to know what happens when a plan of Vetinari's doesn't go his way, even if he is dead.
When Vetinari's man finds Heretofore it'll be to offer him a jobSeriously, Vetinari doesn't waste talent, and Heretofore did manage to go from being an assistant gardener to position of closest advisor to, and manipulating, one of the city's richest men and orchestrating a very neat scam on him. He'll be given an angel deal as one of his clerks.
Moist Von Lipwig is an avatar of Mercury/Hermes from classical mythology.Moist is implied to be an avatar of a god and in classical mythology, Hermes was a trickster and con artist, but was also the messenger (angel) of the gods. He was in charge of lucky finds, commerce (the word actually comes from the root merx) and communication. His symbols included winged sandals and a winged hat.
Mr. Bent is actually a dwarf.That would explain his aversion to light, and his obsession with gold. His unusual gait could be a result of an Igor lengthening his legs. The story about being a clown was just a cover-up.
Vetinari was bluffing about Mr. Pump being able to hurt people.Because there's no Law of Robotics that keeps golems from scaring the hell out of people - and, since the threat was effective, there's no need to actually follow through with it.