Your educational qualifications and what you intend to do after the visa expires are irrelevant to your DTV application. Simply compile the required documents and submit.
No you do not require health insurance for the Non-O visa. Your mistake is that you have clicked on the wrong category of visa when using the e-visa system.
When the program first rolled out there were a number of DTV’s issued for Thai language but since then and for well over a year I have not seen a single post where Thai language as a soft power option was used.