I used to buy these with 300 plus a month cashflow and today it’s 0-150 with sound conservative underwriting.

A very strict underwriting criteria with truly conservative projections is a MUST. 

my question is do FHA appraisals more conservative than conventional mortgages?

The seller believes that appraisers are conservative and give a low value.

I used a very conservative rent estimate to analyze this property based on the comps and the basic allowance for housing in the area. 

So i'm all i for 45,000, I could rent this property for conservatively 900 optimistically 1000.

And let’s also say we can refinance up to 75% to be conservative.

That would be the most conservative and safest way to invest in real estate.

I hope to meter this expense out to tenants but in case that is not an option, a rough estimate would help in running my numbers.I've been googling around and found the following approximations and wanted to see if they are consistent with what you all are seeing:-cost of insurance in VA to be ~$80 (I'm assuming this is for SFH)-vacancy about 5%, conservatively ~8%These are the factors I am not sure of in my calculations.

If not, as a conservative measure, you can use the land/building value split used by your tax assessor as the first step.