2. Language doesn’t qualify for soft power (usually). Thai cooking, Muay Thai, or medical or dental appointments do.
3. See point 2, but you can still learn Thai on a DTV once you have it.
4. Yes the visa is valid for 5 years.
5. Start by checking out the Thai embassy/consulate that you’d use to apply. Their website will list their specific requirements. All differ in processing times. Some are a matter of days, some weeks.
Your passport. A print of the DTV and ensure you have filled out a TDAC. You almost certainly won’t need a print of the TDAC but won’t hurt to have it.
You’ve picked up old information from somewhere. Bangkok used to have that rule where you needed to have done a 90 day report before they’d issue a COR. They stopped that quite a while ago now.
Anyone can get a COR on any visa type.
You’ll need a copy of your passport data page, a copy of your latest entry stamp, a print of your DTV Visa, a passport photo and a printed TM30.
If you’ve been in Thailand for 90 days then you will have needed to file a 90 day report.
You’ll apply in the old 101 office which is the entrance to the left of the main staircase.
[edit] Forgot to mention they’ll charge 500 baht if you want it same day. Free if you wait 7 days.