unless you exit and start over. Which is easy enough. I’m not sure why anyone would be desperate to not use the agent though. Most people use them continuously
1. yes it’s perfectly legal. 2. The banks are limiting new accounts for people who don’t have long term visas in compliance with global banking regulations to limit money laundering and fraud. 3. No you could not be deported or banned. 4. No, you obviously won’t be ‘locked into’ anything. But the agents do great work. Not many people change. And obviously you get to keep control and profit from the 800k in your own chosen location.
If guilt and paranoia would affect you, there are excellent psychologists around to assist
actually never book a return flight unless you don’t like your life or money. I’m a full time traveller for 12 years and never buy a return flight in that time. What some airlines from some locations insist on, is proof of ‘onward travel’ which proves to them that you intend to leave the country within the time limits of your visa
use a local agent in your area (so you can have assistance available when needed) that can access a major carrier like Allianz or Axa. At 67 it won't be cheap and worse at 70, but worth it.