Take your provable monthly income before taxes and multiply by 45%.  

I see tax re-proration agreements utilized or even other methods, such as basing your tax credit off the new assessed value, multiplied by the current tax rate and equalization factor.

Since I don't know where this is, but I'm assuming Washington PA or somewhere nearby I'm not familiar enough with what the caps/gross rent multiplier is there to know how the appraiser would apply the income approach. 

So I take the gross rent and multiply x .60.

The standard method appraisers use for determining construction costs (and feasibility) is to use Marshal Valuation Service cost manuals, adjust for the multipliers, add estimated development fees, site costs, sales commissions ect.

Over 8 as a gross rental multiplier in Sevier County for overnight rental, in nearly all circumstances, will only produce a positive cash flow if the cabin is self managed and/or paying cash (or very low LTV).

Mathematically speaking all of the limited partner's outside basis (80% interest) would have to be multiplied by .63 to compress to 50%.

You need to figure out how many months from close to finishing the rehab, then multiply those monthly expenses by that number (holding costs). $90k of rehab should command a better profit. $90k rehab budget, how firm are you with that?

(These numbers work in my market so I am just using those numbers)$ 8000/ $ 800 = 10 properties   (***Assuming $800 - 900 Per door for paid off rentals)Multiply that by a factor of 1.2 so you need 12 properties to be safe. 

When you hear that property management is what will make or break you, multiply that by 5x for this zip code.