DM/Instructor in Thailand

I've been here in the Philippines for the past 4 and a half years and living in Asia for 6 years.

I speak, as yet, only English - is this a blot on my copybook?
Not really ,I speak only English also , if you're a good instructor it shouldn't matter and I know plenty of instructors who speak English only.

If I certify in Thailand how easy is it to move around SE Asia as an instructor?
Moving around is easy finding a job is hard. If you were a dive shop manager and wanted to make your customers happy would you hire someone who has not much experience and zero experience on the local dive sites ........in my dive shop we never never hire the people who walk in off the street looking for a job because the business is resting on a total stranger who might decide to work somewhere else in 1 week.The same as any other business really. To get a job it's always right place at the right time kinda stuff. Most instructors get fed up with not having work and give up on the dream after a few months.

I know I will have to dip into savings while being certified, will I make that back?
Sure ,if you find a stable job and you don't eat out every night you can build up some very small savings by western standards but big by Asian standards but if you still live in holiday mode you'll burn through your cash. I didn't eat out 5 times a week when I was back in Ireland and I don't do the same here.

As an instructor will I make enough to travel about a bit to another dive spot i.e. another country for work?
Don't hold your breath , to afford that you would need a good dive job and if you suddenly find yourself lucky enough to have a good dive job why would you want to throw that away ? Most instructors I know once they find a stable job stick to it , the ones that are moving around are usually living off a second income or savings. As a side not these kind of instructors who we see moving around place to place every few months rarely are hired by good dive shops. They might find work but it won't be in a friendly relaxed dive shop where you want to stay long term.

Would I be better off getting up to DM here in Ireland while I'm working and then move abroad?
The benefit I see from doing it in Thailand or something is you start making contacts in Thailand or where ever you choose to do the course.Very often doing it in Thailand you might be able to dive for free or something along those lines.

Feel free to ask more questions though. - I don't wish to scare you off but at the same time I don't want to paint you a picture that there is dive shops out there screaming for unemployed DM's or instructors to come work for them.