the first UK person to post on one of the Visa advice websites after getting the DTV wrote himself a letter outlining his freelance income and that waa accepted as the required document.
it's 180 days per entry. You can extend each entry for 180 days for a fee or leave for a brief period, eg overnight, and re-enter for another 180 days in the same year.
Oddly some Embassies say attending a music festival is a valid reason for giving the Visa.
I am from UK and now have the DTV based on a 4 week booking of lessons only at a Muay Thai gym. Not actually sure how short that booking could be and still justify the Visa.
44,460 was last year's uncontrolled migration. All other people enter the country with permission from the government and in line with government controls. That's controlled migration.