depends on your circumstances... DTV ฿500k under 50 but no local bank account. Non O over 50 ฿400k or ฿800k bank account and depends. Elite visa loads of money bank account Non b bank account. Get on the thai e Visa site and see which ones suit you
its the biostatistics. Where did you apply for this DTV? Another problem is if you leave the country where the application was submitted before approval the application is cancelled
VOA is only for 15 days if you mean entering Thailand without a visa or Visa Exempt then thats for 60 days depending on your history you may be allowed an extension for 30 days.
Make sure you have an outward trip within 60 days ฿20,000 or equivalent in cash and where your staying.
Best to apply before he comes. I think (my opinion) is the Embassy website where you wish to apply will want ฿800,000 (or equivalent) in his home bank. Best ask your embassy