Is there a good authority website that allows you to properly estimate appreciation over say, a 5 year period in a specific zip code? 

@Hae-Yuan Chang here is a BP Blog post that explains CAPEX reserves. https://www.biggerpockets.com/renewsblog/2015/10/13/real-estate-capex-estimate-capital-expenditures/You should also budget a minimum of $500 per year for routine or emergency maintenance.  

If you can think of them as part of the broader strategy, it's very likely that 20% will have a rough(er) outcome (just based on a simple Pareto estimation).

Contractors being contractors, it took about twice as long as they estimated because they didn’t have enough people working on the house at any given time (usually only 1 or 2).

If you provide more details of the property (purchase price, estimated rents, rehab estimate, expenses, etc.), people may be able to answer your question better.

I see people paying around Zillow estimates (Bad idea in my opinion), I see investors purchasing right around the ARV, but...

Once I get them up to $500, cap rate becomes 16.7%, cash ROI is 49.9%, and annual cash flow is $10,916 ($113/month/door).Are my estimates way off? 

.-3% down would be around $4,500 down payment-$14,000 savings for 12 months mtg pymt expense used as needed to get the ball rolling-The properties I look at probably need $2000-$4000 in renovation expense-Estimated insurance would be around $120/mo and taxes around $250/mo which is included in the monthly total I came up with: $1166 roughly.

You still have to worry about market rent rates dipping below your expenses, but even then, in a house hack situation it's still likely to beat the alternative: paying rent in an apartment and not building any equity.If you're looking for rent estimates in your area, I've found Rentometer to be the easiest to use to get a quick estimate.

I've estimated $5k for repairs.