I haven't been around here on OCC much lately, but I thought I'd chime in on this topic since I'm currently working in South Korea.
I've been here for about 8 months now, and although it hasn't been all sunshine and rainbows, it has been an incredible experience that I do not regret the slightest. Coming here was a tough decision, because for at least a full year, I would be away from my home, my family, and my friends. But I'm still very young, I'm not married (forever alone) and I don't own a house, car, or have any other major expenses, except for student loans. So for me, it made perfect sense to go work abroad now, before I have many other responsibilities and obligations. I know you just bought a new Jeep, but it's still not quite a life-changing responsibility that should deter you from moving abroad.
If Japan is your first choice, then I'd say study up on the culture before you go. Read as much as you can from other people who have lived there. I traveled to Japan this summer, and even going from Korea to Japan, I was a bit shocked by some minor cultural differences. Also, study as much of the language as you can before you go -- it will make a huge difference. At the very least, learn to read the language. From my experience in Japan, it's a lot less English friendly than Korea. Some of the smaller subway stations will have very little English, or none at all, and getting around can be a pain if you can't read it. Also, I've found that while many of the older business-professional Japanese speak English quite well, much of the younger generation do not. There has been a bit of a push for Japan to maintain its own culture in recent years, and one of the effects of that has been a decreasing amount of English education. But if you learn Japanese, people will be really impressed with you, and they'll see that you're actually interested in Japanese culture and language. So not only will these help you get through things in daily life, it will help you make new friends much faster, which brings me to my next point.
Meet as many people as you can, make friends, and go out as much as possible. I'm quite an introvert myself, but having some friends in a foreign country will really help cope with being away from your home, and they can be invaluable if you ever have any troubles with transportation, banking, or any other issues where communication is critical. I can't tell you how many times I've ended up on a bus to nowhere because the ticket salesman misunderstood where I wanted to go, and then had to call a friend to help me find my way back. Having friends who are fluent in Japanese will be really important to you. Not only can you learn a lot from them, but they will certainly be interested in learning about you.
As some have pointed out already, banking in a foreign country that doesn't use English can be frustrating as hell, but that's what your friends will be there for. Banking with a foreign bank won't be the end of the world. I use a Korean bank, and all of their ATMs and online banking have the option to use English, even though some things don't translate quite well. I send money to my US bank using my Korean banks overseas remittance, and this is where things get frustrating for me, because I'm hit with quite a bit of fees from my US bank and intermediaries. Medical care on the other hand shouldn't be a huge issue. Just make sure that you have health insurance. Not being covered in a foreign country is a scary thought. But thankfully for us English speakers, every medical doctor in the world studies English to some extent. I've had to go to the hospital, a few medical clinics, and even the dentist, and each time we were able to communicate just fine. I live in a small, dinky town of about 3000 people, but even showing my dentist which wisdom tooth is hurting and making a yanking motion is enough to get the message across. The quality of medical care here in East Asia is some of the best in the world, so unless you have any food allergies, or some pre-existing conditions that could potentially be a problem, then you should have nothing to worry about.
Finally, just understand that you'll be in a foreign country for an extended period of time. Your whole life will change and you'll become a different person because of it. Whether your experience is amazing, or completely horrifying to the point where you're penniless and destitute on the other side of the world, you will be a better person with brand new experiences because of it. If there's really nothing you can think of that could hold you back from going, then by all means, do it.
If you have any more specific questions on life abroad, feel free to PM me.