It took me years of work to develop the process i use to identify a range of value for businesses. It also took years to gain conviction about the application of the processes. I also have continued to revisit, challenge and refine how I arrive at a range of fair value. It was an enjoyable journey for me and I hope it is for you too - that makes the financial rewards much more satisfying IMO.
A couple of things i noted in your post, you said,
using average growth rate to extrapolate the free cash flow
I think projected growth rates need to be thought through and calculated individually for the specific business, eg I would probably use a very low growth rate (if I even believed there would be any growth), for a business in decline like Telstra.
Also you don't mention a risk free rate or hurdle rate that you are discounting the projected FCF by, typically I have thought about that in terms of 10 year treasury bond rates or an equity risk premium - again you have to be very careful in the low interest world we live in now and think about how you are going to set that rate very carefully.
Overall I believe an investing strategy and process needs to be articulated, documented and generally followed. It needs to be a strategy of parts, the final part of which is probably the calculation of a range of IV, to see whether the price is attractive enough to warrant an investment. I try to avoid reading other people's research or opinions as part of the process, I want to own the decision 100%. My process involves identifying small and microchip businesses that are profitable, largely debt free, history of stable growth in revenue & earnings, illiquid, founder involvement and well managed.
I turn over a lot of rocks looking for investible businesses, occasionally I find something interesting, very rarely I find something that ticks all the boxes and is cheap!
I believe its a very personal pursuit, there are many different strategies and processes that you can use, all of them will have a small % of proponents who outperform the market consistently over a long time. I suspect part of the reason for outperformance in a chosen approach is discipline to follow the approach and conviction in it. Good luck with your journey!