sorry I can't remember which group it was in. It was the second post I read about someone getting a DTV and it was in the first 3 days of the Visa being available.
One UK freelancer wrote a letter himself saying he was freelance and the type of work he did.
A US freelancer posted he just had to screenshot some work samples, provide a sample client contract and highlight money being paid into his bank account.
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.