If you don't, I am sure there are firms that specialize in this...the great thing is that most do not get paid unless they are able to successfully lower your tax bill.Best of luck!

Are there real estate agents who specialize in this area or do I prepare my own offer? 

I don’t know where to find one that specializes in rent control laws, as the research i have done already all the lawyer sites around here say they help the “poor tenants affected by horrible landlords”.

What has been your experience with surprise HOA "special assessments" and other dealings with the HOAs?

I think the best flip opportunities are present when there is something special about the location or style of the house.

I specialize in multifamily homes, but I'm looking to flip single family homes to build a stronger multi family and commercial portfolio. 

I'm currently running Facebook ads directly to my mailing/ call lists bypassing the need for the special ad category.

Reno/make ready costs are pretty high still and taking longer so it makes sense to keep tenants around, specially if they’ve been paying on time.

I would reach out to a local RE attorney who specialized in evictions as like you said the courts are very backed up and youll have to still go through the Diversion Program (https://eviction-diversion.phi...). 

The contract had a special stipulation indicating that buyer is willing to pay $5k over appraisal if appraisal is less than offer price.