There's a million of the same stories out there, so really, who cares about what I have to say but here you are.
Been living here for 9 months now (Yokohama). I do the whole teaching English thing in a public school as an ALT. I'd never stepped foot in Japan before I came here. I'd never worked or lived in another country. Honestly, besides some art, games and films I really didn't have much perceived emotional attachment to Japan. I didn't really plan on visiting anytime soon, but like a lot of people, I just wanted to do something different. I wanted to live in another country, meet people, learn a language and challenge myself to do something without all the comforts and safety nets of my life back home, because there were a lot of those. Anyway, this entirely from my perspective, so teaching English but wanting to find a more appropriate line of work for my skillset at some point in the future.
I really enjoy my job and teaching, but have had to reset my expectations many times. Granted, I got placed in one of the worst schools in the city, but school and teaching culture is SO different here that if you can't change the way you think about things, then you'll end up miserable and bitter when things don't go your way. This is easier said than done but If you can adjust and change, then teaching can be very satisfying and enjoyable.
For a lot of people though, I think it's a slow creep, they never wanted to teach, and by the time they've realised that they're deeply unhappy they've fucked themselves completely by not studying the language and more importantly by not having any marketable skills. There's nothing wrong with the guy who flips burgers by day, but goes to night school in the evening after work. The reality is a lot of people flip burgers by day and go to the pub in evening.
Besides JET, I don't think there are many golden egg teaching opportunities here, it's not worthwhile to think about it as a long term plan. Besides, there's a culture of employee turnover and just as soon as you've settled into something you like, you might get moved on to something against your will. That's how it is. When it comes to job stability and visas, you could be working here for ten years and have the same security as someone who has been working here for 2 months. It's not the reality for everyone who comes here but for many it is, especially someone new to the country. Is it something to get angry about? No, not really, but some people can't let it go and create an image of themselves as the perpetual outsider, with Japanese society a huge wall blocking you from getting in. Which is wrong of course.
Another thing thing about teaching. There is absolutely no standardisation to it at all. One guy might have a bunch of teaching qualifications and experience, and another might just be some dumb kid with a media studies degree and that's it. It's not to say that both can't be ultimately end up being good teachers, but it's more than likely that the person who cares more about teaching is going to have a better time of it. They are going to be able (and want) to match their expectations to the students ability and culture of teaching, and ultimately adjust to the way things are taught. Teaching is all about giving, it's a selfless pursuit with little reward. In terms of workload, again, no standardisation, its all down to luck ultimately.
On the whole Brexit, intolerance, dumb people thing. You need to change your expectations on that too. I've been stopped by the police twice for no reason and asked to show my ID card. Been shouted racist stuff by a crazy woman in a train station, and obviously all the usual silly micro-aggression stuff which Japanese people just can't help but do. I don't take any of this stuff personally, so it doesn't bother me at all, but some again people can't let it go and it inflates their sense of negativity, and way they choose to interact with people.
Most Japanese people above a certain age (I assume the age group you would be targeting as friends) work crazy hard. No one is going to fall over themselves to be your friend. Someone was complaining in the Japanese learning thread about how Japanese people are flakey, but 90% of the time its because they're dedicated to their jobs and really don't care enough to babysit a foreigner, order food for them and do the most basic things for them. A lot of people just don't want to speak English all the time, even if they have the ability to. You have to work hard to make friends, and keep making friends after that.
In summary, I like my life here and have no complaints at all, but its nothing like my life back home. I accepted that life my world would be turned upside down and that I'd have to start from scratch in a place that wasn't my home. Anyway, maybe to answer your question more succinctly, I used to do freelance and part time teaching in the UK, and I think could easily live that lifestyle here. My second year is going to be so much easier but I still have a lot to do if I want to achieve my goals. Maybe that's the most important thing. What's your goal?
Just in terms of overall enjoyment of living here, Japan is a great country and I've had a blast so far, but with many of the ups and downs that go with uprooting yourself completely. Your ability to cope with such moments just depends entirely on your attitude and resourcefulness.
