You don't need to leave Thailand every 6 months but atleast every 12 months, but with all the paperwork you need to extend 6 months on IO and you need live up to all requirements again when extend at IO. Much easier to use 1 day fly out and in again same day on a cheap plane or do a border run. I would anytime leave Thailand 1 day to get rid of paperwork and all the requirements you had when applied for your dtv visa.
As far as i Know Denmark have not changed as other embassies, that money needs to be in bank/banks for months since I got my DTV statements only needed for the day you send application and applicants name need be on statements. Atleast not changed on thai embassy Copenhagen homepage yet , and it's that embassy that approv your visa as long you are in Denmark. You can only apply for visa online in Denmark true the official thai e visa system, no visa is issued in person,
Now I remember, I had a challenge too with payment, had a browser issue, I logged on my e visa account with another browser, I recall it as payment come in a popup and my first browser blocked the popup
I merged pdf documents into 1 document when I needed to send more than one, I needed it when my 500k was on 2 accounts, it was the embassy I applied at that said I could do that
With dtv visa income don't matter only the 500k bath on your personal account/accounts on statements that is required, check up on how long time it's required the money is on your account on homepage for thai embassy UK , different requirements from country to country you reply from , some it is 3 months some it's 6 months, when I applied from Denmark it was the day I applied, Can have changed
I would ask to see the bill , in my house I get the bill in my mailbox at gate of my house, if not a mailbox bill is normally next to meter when the guy from power company make the monthly bill. If I remember right a thai friend of mine that have a resort told me he calculates 100-150 bath a day when customers use aircon in rooms/bungalows and they are not isolated