What you will find though to watch out for is that somewhere down the line, maybe around year 7-10 depending on interest rate and amortization length, the interest portion of  your payments will go down enough that you no longer have a 'tax loss' any more (but you are building equity faster. 

https://www.washingtonexaminer.com/look-at-how-man...Here are a few tidbits...74,608-page-long federal tax code.The federal tax code is 187 times longer than it was a century agoAmazingly, in the first 26 years of the federal income tax, the tax code only grew from 400 to 504 pages.Most of the growth in the tax code came in the past 30 years, growing from 26,300 pages in 1984 to nearly three times that length today.Just you know- Keeping it simple lol

I believe that in a non-arms length deal (which this would be), the transfer tax is still collected based on assessed value and not the sales value, but I've never gone through that process.

If it needs to have been a rental/investment property is there a certain length of time requirement?

You will have to pay another transfer tax.Since this is not an arm’s length sale of the property, the transfer tax would be based on the value as determined by a formula that the PA Department of Revenue uses.

I apologize for the length of this post up front. 

Obviously, I don't know the full length of your situation but please look at all scenarios before closing yourself off to opportunities. 

Already have it full booked from December to May however. property: duplexuse: Owner occupied on 1 side and mid-term length rentals on the other side (30-90 days average booking). 

If so, what is the length, of the warranty?

The length of time they are there could be 6 months or 6 years or even longer.