No business accounts are allowed. And yes I would spend time creating a portfolio doc. Mine was 27 pages lol. Don't expect them to visit your website, add screenshots, explanation, etc. You have to convince them basically ;-) good luck.
They don't currently check on re entry so theoretically you can do whatever. They only check when extending in an immigration office so you won't be able to do that but border runs should be no problem ... for now.
April this year. I think if you meet the criteria and present it clearly then it will be fine. I spend 3 days creating a 27page pdf for my application. Didn't get one question. Straight to approval.
Yes I used my kbank account which I opened years ago. I was also in thailand so I went to get the proof from the bank in the morning, flew out to cambodia in the afternoon and applied for the DTV in the evening. I had no issues.