Can you point me to a data point where the safety of a neighborhood has been compromised because of the presence of STRs?

Look at some more but you might have to compromise by looking at less bedrooms, raise your price, lower your standards or try a diff area.

It sounds like a conversation with the investor on their expectation of the deal and perhaps compromising.

I hate to be pessimistic, but the thing you have in writing says you have to pay the $50.Someone on the phone told you not to, but there’s no written documentation of that, or that the person who told you it had the authority to say it, that what they told you was the official and correct policy, etc.I suppose a good compromise would be to email them and ask for written (emailed reply) confirmation that you can ignore that invoice, that it was sent out in error, and that you should not pay it.My guess would be that no one will respond to your email, which to me would mean they’d be unwilling to give you written confirmation that you should ignore the invoice, which would mean you’d probably want to pay it at that point (in my opinion).It’s completely up to you, but that would be my thoughts on how to handle it.Kind of ridiculous of course that you’d even have to apply this kind of thinking to $50, but when the City has the power to attach a lien to your property I think it’s worth being a little paranoid.

Basically, hackers can compromise your e-mail and monitor emails being sent/received.

I was beginning to feel desperate and a few times caught myself compromising my numbers to "make it work".

One is that when there is a failure of some sort, like heaving, cracking, etc - it's systemic in nature and affects how it looks and also makes the structure compromised. 

It's a business and I have given way too much away, compromising the whole reason for doing this in the first place. 

Its started out very promising.... but of course, its become a very frustrating experience when the vision for projects don't align... and project direction mismanaged and is starting to get compromised.  

If you want to optimize for financial return of your purchase, and are ok with some compromises, I'd suggest buying a 4 bedroom 3+ bath house/townhouse in a good location within Hayward, and renting the other 3 rooms out at ~$1200/month each.