I think the best way to go about this is to grow your own business to a point where you have other trainers working for you. If you want to make a good living, not being physically demanding on your body and still help clients reach their goals, I believe this is the best way to approached it. Having your own business will give you the freedom to do the things you like the way you want too. If you have a 5-10 year business plan, you should be able to grow it to the point where not only you can achieve all of the above, but even sell it and make a great profit in the process. You just need to figure out which way you would want to grow your business and the type of clients you want to approach and specialize with.