It sounds like you'll be leaving for Germany very soon. If you can get an appointment relatively soon, you could always start in the UK. I wouldn't suggest it if your first appointment is only a few weeks from your departure date, though, as I don't think you'll be able to accomplish much.
If you'll be in Germany for a year, why not start then? Even if you're not interested in starting HRT immediately or at all, talking with a professional can help. You'll already have made progress by the time you go home. And regardless, you might want to consider scheduling your appointment in the UK while you're still in Germany just to make sure there's not a big time-lapse between visits.
Wishing you the best!