I suppose what I am wondering is, if the work output to satisfaction input ratio is something that can be pre-calculated? Or does it really just come down to jumping in, testing the waters and experiencing first hand, fulfillment or lack thereof?
Did you know you would enjoy photography as a career before you started?
Is it simply a means to a end?
Would you do it if you didn't have too?
I don't think you can calculate out the exact ratio when it comes to work output/satisfaction. You're dealing with people and people are unpredictable.

You will have bad days and good days, hopefully more good days than bad.
I started my business in 2012 and not only that it is my only source of income, I'm also the primary provider of my household. When it comes to the artistic side of a photography business, it can be repetitive. I enjoy both the business aspect and the creative aspect of running a photography business. Before I went full time, I was afraid that by making it a business I won't be able to enjoy photography. I actually enjoy photography very much and my clients love that I'm so passionate about what I do. So, yes I knew I would enjoy photography.
A means to an end? I'm not sure exactly what you mean.
I would do it much earlier in life if I had to go back and do it again.