I’m going to answer your questions with a question of my own! I hope that my question will help you to get it straight in your mind what you really want to do. Do you want to teach English for 6 months and then go back to your current job? Or do you want to continue teaching after those 6 months? If you want to continue teaching and to make a career out of TEFL, it is worth investing in a good TEFL course. If you only want to teach for 6 months, I’m not sure what to say. I’m afraid a good TEFL course is expensive and I’m not sure it’s worth it if you are going to give up after 6 months. This is a decision you’ll have to make.
Having said that, you will be more limited in job opportunities if you haven’t followed a good course. Of course, you can still get a job but it probably won’t be one of the better ones. I won’t advise you on courses you can look at the TEFL training discussion forum http://www.tefl.net/forums/viewforum.php?f=11
where the issue of which course to follow has been covered many times.
Your lack of degree will also be an issue; in many countries you cannot teach without a degree. There is no way around this if you want to teach legally; you may not be able to get a visa for a teaching job without a degree. I think Japan may be one of those countries. I’ve never worked in Japan so I’m not sure. You could put your question in the Employment discussion – Asia board viewforum.php?f=21
I’m sure you’ll get a reply there.
As for having authority over children, that doesn’t have to be an issue. You can get a job teaching adults which means the question will never arise. That will also reduce your anxiety and help with your OCD. I don’t know much about OCD; I guess it would affect paperwork, as you say. It could also affect your lesson planning; new teachers tend to spend a lot of time preparing their lessons; if you feel the need to check everything you prepare many times, you will spend more time on this aspect of teaching.
Please write in again if you have any other questions and do look into the other forums on this site that I mentioned.