Considering moving the family to Japan...Looking for some info

Hi there,
My husband and I would like to relocate to Asia with our 2 year old son in the next 2-3 years.
I spent my 20s teaching abroad and would like to return to Asia, as one of my favourite places.
We've been discussing where we would like to go and we seem to have narrowed the list to Japan, Tawian and Singapore.
I plan on teaching in an international school but we're not sure what the opportunities will be like for my other half. He's a plumber by trade and, ideally would like to do something related to this, but he's also open to doing a tefl and teaching English (he has a degree).
Could anyone advise us on:

1) what opportunities there might be for English speaking plumbers in Japan (if any!)
2) opportunities for him teaching EFL in Japan
3) what can I expect to earn working in an international school in Japan? Would it be enough to support the family?
4) what benefits should I be looking for in an expat package from an international school in Japan?

Another motivation for the move is to access decent healthcare. We're from the UK and with the situation with the NHS at the moment, I've developed chronic illnesses due to improper healthcare during pregnancy and labour. These need to be managed with medication and monitored regularly. What is the healthcare like for expats in Japan?
Any information, advice and tips would be appreciated!
Thanks so much :)

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