You've asked a lot of questions which is fine, but I'm wondering just how much research you have done on the kinds of language schools that exist and will employ you, and the contractual obligations for each school. Generally, language schools get a bad press here, so you would need to be assured that you have made a sound choice. As you don't state whether you want to teach music privately you also need to consider if any of these language schools actually want music tuition as part of the package. My guess, and that's all it is, would be that they don't need this and prefer to concentrate on English.

As for doing CELTA, any of the providers you list would be OK as they are all established players. I did my CELTA at a university school of modern languages, so my choice would be UCL if I was in your shoes. This is for the simple reason that you will more likely be taught by experienced linguists who will probably be teaching foreign languages as their normal job. As part of both the CELTA and Trinity TESOL courses you will be put in the position of an adult language learner. In my case we had Japanese lessons, which were fun.

If you don't mind me saying, you seem to have a lot on your plate with all the coursework and theses, and getting this completed would be my priority.

You also don't indicate why you want to do a PhD or what you will research. Do you see yourself working in a music-related field or in language teaching? Or is language teaching just a way of earning some money until you go to Berlin for doctoral studies? As you are in the UK, I would have thought that doing a PGCE (Postgraduate Certificate in Education), would have been a good choice if you see teaching as a future career.

Gosh, if my background was similar, I would be teaching music to the kids of rich parents, in Beijing! If you have a 'social conscience' then there are also opportuities to teach music to kids who don't have rich parents.

I have a Chinese friend who in fact acted as my agent (free of charge), when I first came to China. We taught together at one time. She is a superb pianist, (at least the equivalent of LRSM Grade 8 or higher), and now works in a conservatoire as an assistant to a Chinese professor who teaches composition. And then there is another friend, in the UK, who now works as a periptatic music teacher. He was a part of a local band but wanted to try teaching. With long blond hair and a full-length leather coat he walked into his first classroom with a 1960's Fender Strat in one hand and a practice amp in the other. After playing various solos and licks from Joe Satriani, Clapton and Hendrix, the students were spellbound, and he was offered a permanent job which was when the real music teaching started.

Perhaps other posters can pick-up on some of your questions.