Make sure to put in any and all things you don't want, loud noises, smoking, dishes, and when and how to wash and dry clothes.

Is there any workaround may be more labor-intensive where I could find these phone numbers and addresses linked to the properties for free

Since you're in Long Beach, how will you manage your fourplex in such a management intensive city? 

If it's after hours, you can call the police and file a noise complaint.

There will be more traffic to the rental, more wear-and-tear, higher risk of noise complaints or parking issues, parties, etc.

@James Sloan As opposed to most people here, I'll say new construction is a smarter move albeit much more capital intensive and riskier.

I am very fortunate to get the opportunity to attend dental school with no debt out of my own pocket, but I fear that 4 years of intense studying on subjects that are not that useful in real estate will not only wear me out but also stop me from learning about real estate overall for 4 years.

Burbon Street was a cacophany of noise beyond the decibel of painful, not the smooth jazz, ragtime, creole, dixieland and so on.

Block out all the noise.

I like your point about insulation and noise above us.