Next you should have someone with the needed expertise (contractor, engineer, architect) examine the house to see how it could be divided - depending on how the house is built, you can end-up with some strange layouts when you start sub-dividing a house.Should I split this SFH into multiple units?

@Alex Chau  Here are the steps I would follow:Hire architect, have them draw basic planssend architect to the PLANNING department to further refinement of designget plans approvedhire a contractor to build home and get inspectionsDecide how to best capitalize on your Additional Dwelling Unit  (ADU).

Architect - You would need an architect to provide you a general idea of what you can build on the property or you need to be aware of setbacks for the said property5.

Hello,Looking for any local engineer, contractors, architects in Queens/Long Island, NY.

Needed Permits, Architect and Engineers.

. -- getting More-than-ONE-architect-to-call-me-back in this incredibly busy Chicago market [two architects just plainly threw me the $10k bill without even talking to me over the phone!

@Henry Lazerow - We work with a couple of architects that are leading the way with Chicago ADU units. 

Building a coach house would be neither cheap nor easy and you would need an experienced architect & contractor on your team.If you're not seeing properties that make sense within your budget, you should consider lower cost areas.

Some of the best ways to find contractors is to talk to architects, designers, engineers, realtors, property managers other investors, Facebook groups, supply houses home builders association and other contractors. 

Likely an architect or local attorney could help you navigate this.