I don't see that as a drawback. I don't know anyone who is really interested in paying large sums of money to become a permanent resident of Thailand. There's no significant advantages
Excellent! I switched from non-O retirement to DTV in October last year. Best visa ever. In about two years there won't be many left on non-O, many retirees and marrieds will make the switch. Makes perfect sense
There is an interview at the respective VFS office in Bangkok, although it's more to do with gathering biometrics and confirming documentation. VFS is merely the agency which collects the information on behalf of the embassy and is not involved in the decision making process
You apply online. All an agent does is charge you money to complete the online form, which is simple enough. I've done it three times for my partner. Germany, Switzerland and France. Very straightforward. Answer the questions and attach the requested documents
is correct. Any capital gain in another country is not taxable in Thailand until the proceeds from that sale are transferred into Thailand, and even then any tax already paid is a deduction against Thai tax, which for many countries might mean no tax is payable in Thailand