All of those examples help with sponsorship application. Must submit bank statements, highlight income for ease of approval. Can be easier to " borrow" the money from dad and apply yourself
DTVs have been given for newly formed business with no income. You should demonstrate another income stream e.g savings to show you can support yourself while the business takes off.
Your second entry will extremely likely be like your first, no questions asked. The recent changes are not for visa holders. The 2nd entry is not automatically harder than the first. Many have entered 5, 10 or more times with no issues. Having your MT docs to hand is good to have, in the unlikely case of being asked.
You will be fine with your DTV..I have never been asked in 7 arrivals to show the 500k THB in savings and don't expect to be asked when arriving next week.