My school also has adoption leave that is the same as maternity leave.

Yes. I've done it, as have many others at my school. There's a FB group for expats who are adopting in China, as well as a WeChat group. Highly recommend both of those, especially if no one else at your school has adopted (or adopted recently--it's a very different process than it was 10 years ago).

I can't answer most of your questions, but I have successfully gotten years spent teaching internationally counted domestically. My state's Dept. of Ed has an experience verification form that I had my last principal fill out before I moved on from that school. So long as a school is regionally accredited (WASC, NEASC, etc.), my state will count it. Those years got added to my teaching license. I found the forms online. Maybe California will have something similar?

I don't know the answers to all of your questions, but I can say that I know of at least one large, Tier 1 school in China hires Chinese teachers as overseas hires if they have foreign passports. So if one does it, others probably do as well.

It seems like you've more solidified your plan, but I thought I'd add a bit of my own personal experience, since some of my past mirrors yours. I also initially got certified in a classroom teaching area. I taught overseas for a bit in a position that didn't really "count" either. I decided to go back home to get "real" teaching experience. I did get hired via phone (this was back when Skype was too new for widespread use). Then I got my M.Ed in ESL while home. I've been abroad for years now, sometimes teaching in my academic area, and sometimes teaching ESL in the primary area. Don't be fooled, most intl schools have ESL/EAL positions. Good luck!

My best guess would be a combination of two factors:
1. An explosion of international schools around the globe. Take my current city for example; ten years ago there were 5 international schools, all of which were decent to amazing. Now, there's more than 50 international schools. As you can imagine, a lot of these schools are for-profit endeavors, set up as get-rich-quick schemes by people who have no background in or clue about education. So they genuinely are crappy places to work. This is a trend I'm seeing/hearing about in many cities all over the world.
2. People are more likely to leave reviews (of anything) when they've had a bad experience than a positive one. Human nature.

Do you need to use a company? Do you live too far from a Chinese consulate? I did mine on my own; I wasn't in the U.S. at the time, but another country. I happened to live close enough to the consulate to go on my own (with a few documents mailed to me by my new employers). It really wasn't a terrible process--much less painful than I thought it would be. The worst part was getting the medical stuff taken care of, as the people at the consulate were not very clear about what was required when I called to ask.

The beaches also might appear empty because, for many months out of the year, it's ridiculously hot. You'd think that would make the beaches appealing, but it's so hot that the water feels like swimming in a warm bath. It's neither refreshing nor cooling. During the summer, it's more enjoyable to go to a high-end hotel pool that is temperature controlled and cool.

Yes. Or at least it's been true at all of my ISs. All three have been very different schools, so the reasons might be different, but in all three a lot of drinking happened. In the first school, the staff was quite young and single--lots of drinking. Second school, youngish and mostly single--lots of drinking, even though we were in the ME. Third school--staff skews older and married, but still lots of drinking. This time I like to blame it on the high numbers of Australians on staff. ;)

But for whatever reason, ITs like to ..

I'm certified in multiple states, and had to recertify recently. You'll need to know your state's requirements. For one of my states, providing copies of certificates from different workshops I'd attended was enough. For one of my other states, I needed a combo of those workshop hours plus some credit hours from an accredited university. In addition to the PBS option posted above, I've found two other ways to get credit hours. One is through TESOL online courses, from which you can get University of Wisconsin credits. The other is through TINT (The Innovative Northwest Teacher), which also has online courses in a variety of subjects/topics. For an extra fee, the TINT classes will net you Portland State University credit hours.

If housing is provided, then you'll be okay. If not, then pass.

I did it many moons ago, and overall it was a very good experience. I did it straight out of college, with my new teaching cert in hand. At the time, I didn't know I wanted to pursue IT long-term, so I wasn't worried about future prospects. I just wanted an awesome year in Western Europe. My position as an intern was as an early childhood TA, and since the teacher knew I was a certified teacher myself, she was open enough to turn it into basically a co teaching situation. Not all interns do this. Other interns work in the office, or work as subs, or hop from one role to the next depending on the day and the need. Each school handles the role of an intern differently.

I don't know if the internship really helped my career, but I had a lot of fun! At the end of the year I wanted to stay on, but couldn't do so as a full-time teacher because I lacked 2 years of experience. So I went back home, taught for a few years while getting my M.Ed. Then I hit the IT circuit again. Maybe the internship helped me get my first full-time IT teaching gig, or maybe it was the M.Ed + years of experience in my home country that did it.

Ultimately, I think the benefits of my intern year are a bit nebulous and not easily quantifiable. I made friends, I saw a lot of Europe while earning a (tiny) bit of money, I learned a new language, etc. I'd say the closest thing to career benefits would be that a) I figured out that I wanted to pursue IT while getting a sense of what that life is like from people who'd been doing it, and b) the experience of working with English language learners helped me find a previously unknown passion and a direction for my graduate studies.

I used a relocation company to help me when I moved with an elderly cat. I had a friend who'd also moved to China with a cat recommend Santa Fe Relocation Company or Crown to me. They were expensive, but worth it to me. There are other companies out there with lower fees. The quarantine will depend on where you go. The province I went to had a 7-day quarantine for cats and 30-day for dogs. However, the Santa Fe people got my cat out the same night we arrived and brought her to my door within 4 hours of our arrival in country. I'm not sure if they can do the same for dogs. I would email a few relocation companies out there for quotes; there are specific pet relocation companies and general relocation ones. Again, the prices might be higher than you expect, but it was worth it to me. Also, I paid for basically every service I could to get my cat out of one country and into another--I'm really lazy when it comes to doing that stuff on my own. You can probably save some money if you're willing to do a lot of the paperwork beforehand on your own.

Good luck! Traveling internationally with pets is rough, but I'm happy I brought mine along.

I agree with Medellin and nikkor; it's all about where you are in your career. I did an awesome location with crap pay for my first IT gig as a 22 year old and don't regret it at all. I have amazing memories! But I'm no longer 22 and I've sinced moved on to a crap location with amazing pay. Is it my favorite thing ever? No. But it's absolutely worth it to me for a few years before I move on to something else, hopefully something with a better balance of the two.

Definitely better in the South than the North, but that's not a ringing endorsement. It might be better air, but that doesn't mean it's actually good air. The best air in China is out West, but there really aren't international schools out there as far as I'm aware. Shanghai air is better than BJ, but again, not good. And because the AQI is better in Shanghai, I find people to be far more complacent than those further north: don't own masks, air purifiers for their home or in the schools, etc. So when the AQI in Shanghai goes up, people aren't as equipped to handle it. At least that's my experience.

The air is definitely unhealthy in BJ, but I've never experienced a persistent cough like you spoke of. Could be just my general constitution, or it could be the fact that I own several BluAirs and religiously wear a mask if the AQI gets anywhere near (or above) 200.