Not much I can add to this. Except that you have violated a number of laws.

[Bruno1949]

You HAVE to have permits for the work. ALL the work! No exceptions, no second chances. ESPECIALLY if you plan to rent it! You do not need licensed contractors or plumbers or electricians but it wouldn’t hurt if they inspected the work and gave their approval before the city inspector showed up. However, you have already compromised the structure, the wiring, the plumbing, and heaven knows what else at this point.

Worst case scenario? The city revokes your occupancy permit, they lock you up for a few months, they fine you a couple of hundred thousand, and THEN they get nasty and make you return the entire property to the original condition on your own dime. Without a city inspection you will NEVER get a rental permit. You will NEVER get power, water, or sewer hooked up. You will NEVER get insurance. You will NEVER get an occupancy permit. You will NEVER be able to resell the property.

At this point all you can hope for is some mercy from the city. You probably won’t get it. They tend to frown on illegal activities of this magnitude.

Permits are not a punishment or a means to generate money from poor slobs. Permits are required because too many people figure “this wall is strong enough” or the plumbing and wiring are “close enough”. If they aren’t they will kill someone. In your case you won’t kill yourselves, you will kill whomever was living in this building.

Being ‘creative’ is good, but not applying for the necessary permits is dangerous, stupid, and illegal. You are not going to come out of this well. Even if the work passed code it doesn’t make up for not having the permits to do the work in the first place.

Sadly, being in a ‘historic district’ would have probably only meant that you had to have the proper paint colors in front and the proper type of front door and window shape. It wouldn’t have affected the remodeling inside. You are about to lose the whole thing and end up owing the city a LOT of money and there is no excuse you can offer that will change that.

You might just as well get your affairs in order and go down to city hall and face the music. With luck you won’t be thrown into jail.