For those that do above $800k per yr in gross profits— what does the marketing volume look like across all marketing channels?

New to the land flipping business and have a couple of questions.. 1. Do you ever put your offers contingent on approval of the lot splits? What other contingencies before closing (soil studies, etc)? 2. Are you putting offers in the initial outreach? I assume not, otherwise would be very difficult to send 5,000-10,000+ messages per day. 3. What are you using for data providers? I am looking to find cheap exports of only name and addresses- something other than Land Portal.