I mean I have seen very clear, directly and inarguably comparable properties sold within 6 months of the subject property left off the list of comps, while larger properties whose square footage and bedroom count pushed the value far beyond what the subject property could ever manage to attain (without adding square footage!)

I like to use Zillow.com or Realtor.com to narrow down an area and housing price range, bedroom, bathrooms and sq footage. 

I'm not sure that I would consider such income from that source in my offer, but keep it mind.I'd also look closely at the residential vacancy with mixed use as often having noisey kids on premises won't be a drawing card, but taht depends on how the building is laid out.Basically you approach a mixed use on a square footage basis as to its use and compare with similar use properties and then adjust for functional or external obsolesence, easier said than done.

Some facts of the house:Location: Nassau County, NY, Town of HempsteadYear built:1929Purchase price: 290,000 in 2013Condition: AverageLot size sqft: 5000Livable sqft: 760I'm seeing several houses in my zip code that have been demolished and rebuilt into new houses with the maximum allowable livable square footage selling between $1.0M- 1.2M.Which is a better option taking into consideration, profit and capital gain tax (assuming my household income of 80K)1) Should I sell this house as is at $450K2) Demolish this house and rebuild it without taking out a loan.

Use a ~1 mile radius with similar properties in terms of square footage and number of beds/bathrooms.

I would aim for house with dual master or mother in law suite plus an ADU as long as it doesn't make the sq footage too high.For a MTR I like a 2/1 or a 1/1. 

By doing permitted work I was able to force appreciation by adding square footage while increasing monthly rent by 40% How did you find this deal and how did you negotiate it?

Always make offers below market value at a price that will make an equity,sell or renovate ( It is imperatives to know your comparable and compare prices, Square footage and condition, calculate the cost per SF) compare dollar value (divide SF into asking price to get cost per SF) Ask "Can you help with financing", even if you get a NO, ignore that and make it a contingent in your offer.

@Rodney Turner Can you turn some of your square footage into a half bath?

How much square footage is the boat, and if rentals were allowed what could this kind of property bring in in your area?