You cannot apply in Thailand must apply outside of Thailand. You must show 500kTHB/equivalent currency in a personal bank account. Digital Wallets via Wise, Revolut are acceptable in many embassies.
When I applied in Taipei in person (Workcation) , there were a few SPers who were told the course was too short or they needed to provide more info on finances/employment. Taiwan seemed stricter on Softpower applicants than other embassies. You are right though; a comprehensive application plus decent income/savings helps a lot with decision making.
DTV great beneifit is the inbuilt multi entry, come and go as you like, i will have done 8 entries by year end no probs. There are others who have done more with no issue.
There are a few recent posts from Frankfurt, 15 business days for approval but can take longer. You should contact the embassy regarding your spouse DTV awaiting approval of your own.