One thing to note is that in Boston a high percentage of the multifamily housing supply is 3 families and you are severely limiting your options by only looking at 4 units.

Don't forget to calculate appreciation, debt paydown, and variable costs.  

(Water supply from the main house, a new drain, a small electrical panel, outdoor washer/dryer).The question is...what's the best way to move forward?

Trying to get a VERY BALLPARK idea of what I would expect a per-square-foot gut interior renovation to cost an investor in San Francisco.By ballpark, I mean I'd be happy with a $50/sf range ($125-175/sf, for example) or even just a high-end number (up to $200/sf, for example).By gut renovation, I mean gutting down to the studs and replacing all electrical, plumbing, HVAC, sheetrock and then all mid-level cosmetic finishes (oak hardwood, standard granite, basic fixtures, etc).Ignore exterior costs since I know those are a lot more variable.I realize that there are still a million variables, but I'm just trying to determine if a conservative number is $100/sf, $150/sf, $200/sf, $250K, etc...Thanks!

Assuming all the total numbers work out the same just to isolate the "number of houses" variable, what are the pros/cons of going with a single large investment vs multiple small ones? 

If I supply a laundry room, I get some portion of the income from the machines. 

If you have an HVAC supply near you - purchase four vibration eliminator pads - get the cork center ones.  

I just can not understand why he will not supply it for us.

Too many variables with neighbors, HOAs, city/county regulations, etc.

i understand all the variables, in the end something is only worth what someone will pay you for it.i was more curious as to know if there is anything different about these guesses on a duplex vs. a single family home.