I am not a genius, so I would rather replicate than attempt to re-create the wheel.

Why not call your county permit department, ask to speak with an HVAC inspector and ask him that question.  

Here is a quick high level summary of things you need to consider before you close the land.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 also need to check with the utility companies and get an idea of availability and cost estimates from them for water, sewer, power, gas, cable, installation and connection requirements, tap fees, hookup charges, transformer location and relocation, power line and power pole relocation issues.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.

@Angela Schoenborn Is it legally permitted to be a multi.

Except all of the additions and upgrades to the house were done without any permits.

Say it won’t be an issue with the lender so long as a permit to convert to a 3 family is obtained. 

The house is gutted and has complete permits and building plans.

The city has stopped by regarding an addition that was done without permits 10 years ago.

If so, were permits pulled & were they installed by a professional5.Are any of the homes rented to students6.Is there a flat roof7.are there asbestos shingles - Heating systems- PlumbingSome companies will not write properties with systems that have not been updated The Year that the following were updated (either partially or fully) would be good to know:- Heating systems- Roof- Plumbing- electricalSome companies will not write properties with systems that have not been updated.

If you do it with permits, expensive material it will NOT be cheap.