.: With the laws that the CA legislation has passed, you could piss off a city inspector and there is nothing they can do about a safe unpermitted unit.Possibly/probably....but I think the point we are all making is - why take chances on losing time and money and stressing yourself out?

There are also many calculators out there that over estimate the cost assumptions or rent comps.

Yes I think estimating 5% would be a good start and then once you know the school district you can get a better idea of what to expect.

There's a good chance the issue(s) you face has already been discussed and answered.Ask questions in the appropriate forum.

It’s a good move to have a contractor walk through before making an offer to estimate costs and timeline. 

I have a little hard time estimating a fair market value given these conditions as I don't know how much to discount the value of the house with these issues presented.

Would my previous industry experience (property management, acquisitions, asset management, Realtor) improve my chances of qualifying for a DSCR loan?

If I hadn’t been an expert in this market there would have been many variables I would have had to estimate which is a rookie mistake.

No one in my family really does real estate except for my mom which rents in PR and a couple houses in Dominican Republic but these were things that happened by chance (DR houses were inherited and PR was our primary residence when I was little) ...  

With risks bring the higher chance the cards will collapse.