Hey there. In terms of discounted cash flow analysis, I mostly use Stratosphere.io modelling tool. I used to have a spreadsheet, however getting to know Braden and the platform over there, I have found the tool exceptionally useful because as you said you need, it plugs all the basic data in for you. I am not sure if the modelling tool is available on the free version or if you have to pay for it. You could check it out.
As to how we do the modelling, that all comes down to experience and just getting a handle on understanding how a business functions. DCF analysis is really nothing other than predicting future cash flows. That is why I can have a much different price target than you on the exact same company.
I typically find most people who get into DCF analysis and calculating intrinsic value are a little to optimistic to start. This causes them to see upside in nearly every stock they are analyzing. Once you start to gain experience in running these calculations, you're going to find that identifying an undervalued stocks is actually a rarity.
There are also situations where one can become more confident in their decisions simply based on historical analysis. For example, Well Health is a company that is currently well on its way to profitability and should be consistently profitable in the future. However, there is absolutely no historical basis in terms of cash flows, so predicting those future cash flows becomes more speculative in nature, and thus fair value price targets are not all that reliable.
Compare this to something like Apple, which has a consistent history of generating cash flow, and it becomes easier to predict future cash flows.
Share buybacks/issuances, debt, capital expenditures, inventory (in some cases), etc. all have to be estimated in a proper DCF analysis. As to the accuracy of your predictions, that simply comes with time.
Check out Stratosphere's modelling tool, that should give you a pretty good head start.