I'd send out 500 at a time, using a different mailer/method weekly.

And while nothing is foolproof the most consistent method of finding good vendors is relying on OTHER real estate investors that have worked with those vendors. 

Many opt for other investing methods in their SDIRA like private lending, crypto, private equity...anything except collectibles and life insurance.Note that a Solo 401k is exempt from UBIT on leveraged real estate so if you have self employment activity and no full time employees save for you and your spouse you should consider the Solo K as an option. 

There are also people who swear by one method or another.   

What are the best methods to independently verify zoning and land use data to ensure compliance with local regulations?

What's the highest success percentage method to find a previous tenant's new address for this? 

If you are open to non-traditional methods of financing, you could use a debt service loan to bypass that requirement.

I want this to be acceptable long term if I keep this method of financing. 

I’m also in the early stages of exploring real estate investment, and it’s been helpful to see how others incorporate different tax strategies and asset protection methods.

Each lender can use their own methods of qualification on commercial properties, and most look mostly at the asset (with the exception of your FICO, experience level and reserves).