I am like you. Recently, I was given the advice (by someone who the advice was working for well) to hire a business manager. You do what you are good at (producing content, conducting research, giving workshops & lectures) and they manage the business. You need to be able to trust them, but assuming you can find somebody like that and afford to pay them, it makes a lot of sense. Perhaps there should be an app for that (outsourced business management??).
I'd love to! But, the 3 people I've approached about it so far have all failed to work with a single lead. Literally I'll forward them an email asking me to come speak somewhere, and they never communicate with the person or me about the work again.
If anyone on HN wants to start a speakers agency for tech/security folk, I'd be first in line to sign up :)
I'm interested in your need - in your example, you have a verified, paid speaking lead and you need someone to line up the work for you, get it billed, maybe find you other leads, what else? I'm not going to promise anything other than to think about your need and see if I can come up with a simple solution (I have an idea in mind). If you'd like to email about it, send me a note - noj AT dimensionsix.com.
Best of luck to you :)