My desire to teach English abroad mostly stems from an interest in reconnecting with my birthplace--while I am genuinely interested in teaching, it's not my primary reason. At this point, I'm just shopping around for suitable certification programs.

My biggest concern is that I have absolutely zero teaching experience, and am not a confident public speaker. Does this inherently prohibit me from becoming a good teacher, or is this something I can overcome with enough experience? Did any of you start out as 'introverts'? If so, did your certification program/initial teaching hours help ease you into feeling confident? Or is this something you still struggled with even while you were actively teaching? I'm not like an agoraphobic hermit or anything, but I just never had enough experience with public speaking to feel comfortable, and I get nervous in high-stress situations (e.g. job interviews). Is trying to teach just a bad idea for someone like me?
Being introverted certainly does pose a few issues, that being said, I witnessed a lot of introverted people start off rather poorly but had completely changed by the end of the year.
One thing that really helps is to watch others teach (obviously, if they are good teachers it helps). There are so many techniques for controlling kids and keeping their attention, once you have them down then your life will become much easier.

Kids are kids and if they can spot some weakness or lack of confidence they will often take advantage. Remember how you were when you were in school and the substitute teacher came in? You could sometimes see their lack of confidence and that often dictated the classes behaviour.

I went to Korea with zero teaching experience (although I was not bothered about speaking in front of people). My first few months were tough but I had some great energetic co-workers and became very comfortable very quickly.

I'm sure you'll be fine. The very fact your posting here shows that you'll take the job seriously and be keen to learn. Go and have fun!
Hi. I'm also pretty shy and I'm just starting out in teaching, but I can tell you that the CELTA course that I did this year has helped a lot with the introvert in me. Apart from giving a solid footing to start teaching, so you know what to expect in the classroom and how to prepare and what you'll be teaching and various methods for how to teach it, you also have to stand up in front of a class for 6 hours overall (my course was 8 x 45 minutes, others do 6 x 1 hour) and apart from teaching genuine students (yes they're getting cheap courses but they're still there to learn) you're also judged and marked on every moment you are in front of your class, whether you're talking too much, too little, pidgin English, over-simplifying, over-complicating, whether the students are actually learning what you're trying to teach them, and whether your lesson is sufficiently well planned and executed. It's horribly nerve wracking and quite frankly you've got enough on your plate without worrying about being introverted, and you just forget yourself and get on with it.
It's a really stressful course and the workload is pretty heavy if you're committed, even if hardly anyone fails, but if you need some self belief I'd certainly recommend it.
Best of luck
Rachel