There was a post by a successful Tokyo DTV applicant who had an interview. Essentially they want to clarify what you have documented. Bring your paperwork and just be ready for some questions.
Each embassy has their own approval criteria. You need to contact the embassy you will apply from for their approval criteria and search the relative posts in the threads. Majority of embassies do not approve language courses for the DTV as there is a visa in place for that. Someone posted of receiving a DTV via a language course in London.
Foreign applicants are dealt with quick in Manilla There are a few other countries that treat their own citizens differently in the application process. Anyway, you have the DTV so it's all good.
Yes, you have been very thorough, I noticed you thumbing up my old posts recently. This group is a great resource, i used it a lot too for my application. Manilla is a great embassy i think, you didnt want to go there?