Better call the embassy before applying- I have Spanish Citizenship and i was planning to apply from Madrid Embassy before - I called them and you have to provide more requirements than their website. I applied via Athens instead, having a Maltese resident card ( coz i was living/working there when I applied online ) π
You have to report normaly every 90days at immigration office. If you've overstayed, you're looking at a fine of 500thb per day, up to a maximum of 20,000 thb. Go to an immigration office ASAP, explain your situation, and consider getting legal advice to handle this. π
When applying for the DTV under the "soft power" category, like Thai cooking classes, you initially need proof of enrollment. Upon entry, you don't need to show this again for the first 180 days, but for extensions, having updated proof of your continued participation might be wise- some post in this group has experience already having their DTV extension. However, discretion lies with immigration officers, so keeping documentation handy is advisable. π