@Bill Exeter
It is a Brooklyn, NY brownstone. Single entrance to the building into a common area entryway with separate entrances to my unit just inside and the rental unit up a stairway from there. Units are roughly the same size. Both 2 floors, approx. 1500 sq. ft. per unit. Owner unit is basement (as defined by NYC Housing regulations) and 1st floor and is 2 bed 1 1/2 bath, rental is 2nd and 3rd floor, 3 bed, 3 bath.
It is a legal 2 family as shown on NYC ACRIS system, so I think it would qualify as what you have termed as split use, so from my original example, lets keep it simple and say:
1. 500k current mortgage AND original purchase price, just to keep these simple
2. sell for 1.5M = 1M profit (less closing costs, agent commission, and other fees, but again, keep it simple)
Could I take 500k cash out on the 121 exclusion, then put the other 500k + new 500k mortgage into the 1031?
Also, assuming the answer to the above to be yes, could the 500k cash + 500k new mortgage be split into multiple properties for the 1031? For example:
100k + 100k mortgage for one single family rental house
2 x 200k + 200k mortgages for 2 duplexes