How to protect intellectual property like my coaching method?

If the person doesn't have a patent, trademark, or copyright on the thing you want to copy, then you can copy as much as you want. Current IP law in the USA is "first to file" (see: https://en.wikipedia.org/wiki/First_to_file_and_first_to_invent) If the person has any of those things, and you want to copy them legally then you have to ask them for a licence. If the person has any of those things, but doesn't have the money to sue you for infringement, then you might be able to copy it with legal repercussion. That wouldn't be very cool though.

If you're using source control, it's easy to track source and control access — or revoke access — if someone leaves the company. Also, your developers should have signed a contract about the project itself that clearly places the source code under your/the client's/the company's control, and if/when they leave, they release all rights to code created under that contract. You can never be 100% sure, but these small steps will at least ensure a legal high ground should anyone steal code. Good luck!

This is a tricky question as you are entering a gray area if you are using material from Book Z to inspire your own book. Derivatives works are highly litigated and there is case law that you could turn to to help you make this decision but based on your example its going to be a fine line. You would have to be able to distinguish the products as two very separate works. Since the original book Z is inspiring your new book this may be hard to do. It might actually be easier to talk with the original author about your future plans and develop an agreement between the two of you where he waives any claims he might have here in exchange for recognition in your book. Just an idea--FYI- this is NOT LEGAL ADVICE. You should consult with an attorney in more detail here.

Ries owns 'Lean Startup' trademark. I doubt 'lean' by itself is trademark-able, and isn't claimed by Eric. Someone else may claim 'lean career development,' so might be worth a trademark search.

It's not unusual at all. If you do outsource, try and make sure you have a project lead that you can trust. Once revenues get up to a certain point they might want to see the project through and come on board full time OR they will have enough pride in their work to make sure a proper transition takes place. As far as security, make sure you have an airtight non-disclosure/non-compete agreement with a penalty clause that includes financial remuneration.