With the release of the third book, almost all Bondsmagi questions are answered, so they are summed up here:
Why didn't Capa Barsavi hire a Bondsmagi the moment he suspected he was in grave danger?
Because the Bondsmagi leaders debate and discuss contracts before agreeing to them, so it would likely take weeks or even months.
How can the Bondsmagi function if they are so expensive? Very few people would be able to pay for their services.
The Bondsmagi don't need the money. They have their own city and can take anything they want. They do the contracts to exert their power while limiting their influence.
Why wouldn't someone hire a Bondsmagi to rob Requin?
The cost would likely defeat the purpose as the price of the contract must be suitable. Furthermore, if the Bondsmagi had dealings with Requin they would likely not take the contract due to a conflict of interests. Furthermore, as Requin was holding money for many nobles of Tal Verra, robbing it would have destabilized the economic and political situation of the city-state, which would have harmed the Bondsmagi's assets, holdings, and influence.
Why don't the Bondsmagi rule the world if they are so powerful?
To paraphrase a bondsmagi in the third book "You are so beyond a pig that they can't stop you. So why haven't you taken over the farm and declared yourself ruler of all pigs?"
Furthermore, the bondsmagi believe that the reason the Eldren fell were that they were too fast and loose with their magic and were destroyed by an external force. The current system is designed to maximize Bondsmagi power and influence while limiting them from being too noticeable to any outside forces.
Speaking of the Sinspire—-I wonder if all that cash is really there, or if Requin, being the smart cookie he is, has most of it (except for enough to cover the Sinspire's cash outlays) invested somewhere? He'd probably think it was a wonderfully funny joke for someone to go to all the trouble to break on in there, only to find that there wasn't nearly as much money as rumor had claimed.
It would certainly make sense, and fit Requin's character. The Sinspire is as much a bank as it is a casino, if I recall correctly, and Requin doesn't seem like the type to hesitate on making money by giving out loans.
Based upon the magnitude of the Sinspire (as a bank and a casino), it is unlikely they have ALL the money there. But even if it is just a small percentage (enough to handle someone withdrawing the entirety of their largest single account, for example), it would probably be a massive amount greater than any thief had stolen before.
And based on the descriptions of the vault, it makes perfect sense to keep all the money there. The vault is unbreakable. Locke and Jean are quite possibly the two most skilled burglars in the world and they consider even looking at that vault to be suicidal. And again, it needs to be said again, Requin makes a decent side income renting space in that vault to people who don't feel regular banks are safe enough.
Locke's real name - five syllables, something that surprised Jean - any guesses? Are we supposed to be able to figure out what it is?
It's revealed in the third book: Lamor Acanthus. Although even that may notnote It was allegedly his previous incarnation's pseudonym, so while it's the earliest name Locke understands for himself, it's not the true name of his soul... assuming Patience was telling the truth. be his true name...