Collect people's contact info, share yours, and add them to your database/email list.

I have many thousands of retail owners in my year database built up over a decade of time.

There are larger databases (Co-Star) that have information on larger properties, but I'm personally interested in small to mid-sized multifamily.  

You are talking spreadsheet language in the post that doesn't really correlate to real life unless you are very experienced and using this data based on your experience.

I am also not against registering wholesalers and running their fingerprints through FBI's database, like they do with gun licensing.

Absolutely- the OP was asking where he stores these in his "database".

You need to reach out to the local housing committees they will put you on their database and feed your information to their case workers. 

(I've seen a lot of groups choose this structure)4) Become a part of the issuer (GP-side)I do not want to give other syndicators access to my investor database, so Number 3 seems like the best move.

Start building your database. 

.#4 Before you do any of that while you're prepping to get started is detail out all your databases.