I could be wrong on this, but to my understanding if the work does not affect the square footage of the house nor the structural components, and is simply replacing a "like-for-like" type product (swapping out an old light fixture for a new one, but the are on the same circuit and panel,  permits would not be required. 

This is a decrepit woodlot house built before there was a building code up there and you're comparing its value to new construction built post-1990 based on square footage.

If you go fha to fha they want to have a clear "life" reason such as wanting to move closer to work to cut down commute, move into a larger sq footage unit because you plan on growing your family, etc.  

. - 4 showers and 5 toilets minimum- Minimum square footage needs to be at least 3000 to accommodate everything they need.

If they're within a few dollars of one another, I'd multiply the lower $/ft times the square footage of my investment property and use that as my ARV.If the two $/ft numbers are significantly different, I'd carefully compare the comps to the investment property.

Your home might not be similar but it's all about square footage.

Features such as number of bedrooms, bathrooms, square footage, etc. should be considered when making a determination.Local property managers can also be helpful.

You can justify the value different ways, 3/4 of the appraised value if all 4 units are similar size and value, you can use 3/4 of assessed value, you could base it on percentage of square footage, or you could base it on percentage of rents.

As of now, I'm just working backwards, figuring out from my agent what Sold prices per foot the area can withstand, designing a house with square footage to match the neighborhood, making sure there's a large enough margin between what my turnkey cost is and what I think it will sell for, and then finally splitting what the $ left between what I can offer for a lot and what I wanna keep for profit. 

Just give them your criteria (area - county, city of zip code, building type, square footage, etc .etc.)