Where to begin search for the possibility of replacing an old home with a multi-unit?

[Chris Ghemm]

My mom have a property that's been paid for. Due to her health and age we are considering to let her move in with us and convert her property into a rental.  The house will need a major renovation or maybe a teardown and rebuild for it to be considered safe for rental. It is a small house in a big lot. We are looking at the possibility of tearing down the house and building a multi-unit.  I am not sure where to begin search on how many unit I can place in the lot.

Zoning Code is "M" and County Use Description is "1 Family Residence".