Having engineering plans and calculations can streamline the permitting process, as many local authorities require this documentation for ADU conversions.I can't give an invoice estimate as I am not well versed in how engineers price their work, but I would assume something around $5,000 for engineering services on a project of this size.

It would be even better if we could get it zoned to rent out the house as a 3/2 and separately rent out the ADU as a 1/1.If anyone that sees this has done something like this in Columbus, we would love to get any info on how the process went, how much did the permits and inspections cost, etc.Also, if anyone knows whether or not we could even rent out an ADU through sec-8 that would also be helpful, as we will definitely consider using sec-8 to rent out the property if it can get us higher rents.We are going to be contacting the city's zoning dept right away to verify with them that this would even be allowed at this address, and to try and get a rough estimate of how much permits etc will cost us.

When I originally did permitting on the main house I thought I did it for the detached garage but I didn’t.

These were all have to be corrected and remediated by the buyer with all permits. 

Short-term rental is any rental less than 30 days and is subject to the primary residence rule and require a permit.

If you can do this non-owner occupied, you can look into hard/private money (they will usually not permit owner-occupied).

Investors should be able to apply for and receive STR permits under the same rules as owner-occupied properties.

Cannon Beach generally permits STR but one one occupancy per 14 days,  Arch Cape has a similar limitation with one occupancy per 7 days and Manzanita currently has a fairly long waitlist. 

I sourced the vacant lots, got them permitted, got the financing lined up, built them as the GC, then my wife leases them up and property manages.

I believe assisted care living is covered as automatically permitted in residential (assisted living considered residential - hospice is not residential due to being transitory).