Although I could move out and turn my 3 doors into 6 doors, zoning restrictions require getting permits after you hit a certain number of strangers renting out the same house.So, I think I will keep the same setup I currently have today.

This is a small project and should prove attractive to several banks if you are a qualified borrower.From a feasibility standpoint the first thing is to check with the city or county to determine what is required for all approvals including site plan and building permits, proffers, water/sewer tap fees, bonding requirements, inspections and CO process and time frame for all approvals.You mentioned utilities are in place but you need to need to check with the utility companies and get an idea of requirements to connect to the water, sewer, power, gas, cable, installation and connection requirements, tap fees, hookup charges, transformer location and relocation, power line and power pole relocation issues etc.Check to see if you have to install any manholes, fire hydrants, curb, gutter, sidewalks, street signs, street lighting any specific street design or access requirements,.Check DOT requirements for access, stop lights and permits, traffic studiesDWQ requirements for permits, permit fees, time framesThis is a broad overview of the process and your civil engineer can handle all of this but it's good for you to know exactly what's required.

Call the Building Dept. in the jurisdiction where the property is located and ask them if the triplex was permitted as a triplex.

I know in some areas the zoning only permits a certain amount of unrelated persons to live in one unit.

And they (state and local governments) are still doing nothing to close the gap on supply, while increasing construction/permitting/carrying costs. 

Pulling proper permits are very important and also understanding the rules and regulations of the township.

I am considering building another structure if county will permit.

The hardest thing I have seen about this is utilities and the permitting.

@Nick Seginowich I don’t know what the energy code is like where you are looking at the house, but pulling a permit for a full re-hab may trigger updating the insulation, air sealing, windows, etc to a higher efficiency (which can be costly).I would make sure to do your due diligence before pulling the trigger

Never pulled permits like he should have and showed me a fake GC certificate.