I actually gave myself almost 100k buffer in the overall build cost just to make sure it covers all the extra cost.

Typically you would offer free lot rent and maybe even a few hundred dollars extra per month depending on how many duties you need the manager to carry out. 

It may sound nice to pay a 5% management fee but the extra fees can add up to be more than the other company that charges 10% with no add-on fees.

If you can refinance it and use the funds to then go forward then you already have an extra property by not selling.It is hard to predict the future - nobody predicted a pandemic - and so if you have cashflow then I say stick with it and refinance instead. 

I first go the extra mile to help them most reciprocate those who don't aren't worth the time to type about. 

There was ALWAYS extras...Just don't count on them to respond quickly to an emergency.

Do I charge extra rent in case she not telling the truth?

Whatever thickness you get, try to get it with padding so you dont have that extra cost in material and labor

For example if I do a fha loan and my down payment is around 5k, how much extra should I have saved for this ?

It affects all their income not just the marginal return a few extra units can bring.Anyway thank you all, this has reassured me of my strategy.