As psyguy mentions more information is needed to give any kind of meaningful response. Salaries vary massively between schools. You also need to factor in 30% inflation, currency controls, inept government, upcoming elections, rising crime of every kind and a completely different education ethos that many expats will not be able to align with.
Beautiful country and people but I wouldn't touch it with a barge pole at the moment.

Contracts are 2 years.
Salaries range from 400000 hkd - 700000 hkd / year for teacher. Leadership scale is additional and separate.
20% taxable gratuity at end of each contract
Housing is approx 8000 a month and won't cover rental costs
Flights are only provided at the start of contract
Medical is ok - used to be excellent with bupa now it's ok with good coverage but co-payment
Tax levels out at approx 15%

I worked for ESF for 6 years and left a couple ago. Professionally it was a great experience and I loved HK.

For some countries you can only get a work/residents' visa when you are physically in the country. Therefore you may have to enter on a tourist visa with the school converting that for you when you are in the country. Others can be processed before arrival.