We have sent countless millions of offers to owners since 1999 using assessor data consolidators like RealQuest Pro (the back end of Listsource).For houses I current filter1.

Is there a site or source that compiles data on the mortgage debt that we could look and analyze.

Third-party sites play fast and loose with your data. 

Look them up on assessor data base and mail letter directly to their home address?

If you're happy to park some money for 30 years in an A-class property with professional management and collect a 6% return, then you can do basically nothing.

This actually sounds nice, since it means that the downpayment can be collected in a more relaxed manner, but its also tricky for obvious reasons.Is 8% of the total monthly rent a lot?

And to answer your final question, if you didn't use the application fee you collected, California law requires you to return it. 

I like participating in the program as it works well for my business, but if I ever have to evict a Section 8 tenant it's highly unlikely that I would be able to collect against them in court, although eviction is an unlikely outcome for a properly screened tenant since they would lose their voucher and most would seek desperately to avoid that.

Just want to make sure this checks out before I go bidding on a property. The Owner's Right of Redemption is only for properties that have been owner occupied within 90 days of the Tax sale. So if bidding on a vacant ...

@Jon Peterson I always like to start looking at data.