Keep in mind, if your house is residential (USA), a lot of restrictions will probably be slapped on that would not apply to a commercially zoned house.
For example, your neighbors will probably be allowed to voice their displeasure (hearing), you may be allowed only a tiny sign affixed to the house, sprinklers installed, architectural drawings, lawyer, kitchen issues, setbacks, parking restrictions, #rooms restrictions and a lot of other stuff.
And you can go through all that and easily be turned down.
It is anything but a formality.
I would start with going to the zoning office, and get the code book or the site that has the code, and find out the zoning classification of the house (R-1, R-2, agricultural, conservation district, etc. etc.) and LOOK UP the permitted, conditional and forbidden uses.
Does not matter what anyone promises or assures you. Your house's zoning + "use" will be the final word on whether even worth pursuing..
I forgot to add - the biggest headache we are facing is septic. Around here, once you exceed 700 gallons capacity, you have to do a "septic plan" which they said was 6 months "optimistically".
For a 3 BR house, it requires 400 gallons. Therefore, we would be required to add 100 gallons for each additional bedroom. Any outside visitors (such as having a salon, spa, retail, etc.) requires an additional bathroom, adding 400 gallons capacity required. 800 gallons, if you need men's/women's bathrooms.
In other words, if you have a small septic, keep any expansion to 700 gallons, else you are facing a lot of pain.
Also, once you exceed 5 guest rooms, you are subject to ADA requirements. B&B with <= guest rooms, owner occupied, single building is exempt from federal ADA requirements. You would also need to check state/county/local for any further limitations to this...
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