You can use statements from multiple accounts worldwide just they have your name, I used statements from my thai and Danish accounts with more than what equal 500k thaibath no problem with it's different currency
How can muay thai gym say what the different embassies require, contact the different embassies yourself and ask . It's not the muay gym that approve the visa.
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,