Well @Steven B.I think, this question is what fuels the fear of many who are stuck in the paralysis of analysis. What happens if your analysis is wrong and your actual numbers don't match your projected numbers? ... Can you stand the thought of that? It is always an estimate ... ALWAYS. No matter how much experience or expertise an individual has, it's all based on estimations.
You have to trust your judgment at some point and pull the trigger. I am not an advocate of "jump in and buy something and figure it out as you go." IMO, you have to understand valuation of real estate before all else. Without that understanding, you don't know a good deal when you see one. Make your decision(s) to invest based on strategies that you understand.
Be conservative and leave a margin for safety (error). That means use the high end of estimates on costs and the low end of estimates on values. If that leaves you with the potential for profits, you have a deal with good potential. There are a plethora of details to solve that equation, but that's it in a nutshell.
If I told you, following my strategy, I usually end up making more than my projections, would you stop lurking and invest? If I told you I still ended up falling short of my projections, would you continue to just lurk? No matter what anyone says here or anywhere else, you have to TRUST YOUR OWN JUDGMENT!