I've tried to estimate high for most expenses, sort of planning for the worst, so I anticipate over time I might be saving more than is necessary.

I wasn't anticipating forced appreciation.

Based on area comps we anticipate a return of 8-10% after all closing costs and fees.

Been paying almost 6 years of home warranty on our first property of about $360 for first 3 years and now $720/year in anticipation of a HVAC failure (HVAC was 15 years old when we acquired the property), which amounts to $3.2k in sunk cost.

I would be happy with an overall average of $140 a door, that would land me exactly where I anticipated, using other metrics.

Then you've got to see what your'e true gain position is - The net sales price you anticipate minus the adjusted cost basis of the property. 

The game played from Far Rockaway to College Point, from LIC to Douglaston is pretty much the same:  anticipating appreciation.Sometimes you can 'force' some appreciation by fixing up some units, but the rents WILL NOT cover your expenses.  

I spoke with a lady about buying her home "owner finance" and after putting the numbers in, I realized that I would have to offer her $20K less than what I had originally anticipated to be cash flow positive.

@Rick Zink  Yes, repairs will come out of the deposit (~19xx) but I am anticipating the necessary repairs will exceed the cost of deposit.  

Review it and see if you can pull out the questions based on the anticipated benefits: https://www.biggerpockets.com/blogs/10850/73477-wh...If you need help, feel free to reach out.Best!