For England (High School is 11-18):
1) As in the US, there is a shortage of teachers in England. It depends what subject you are interested in teaching and where you are willing to teach though. English has been officially a shortage subject in the past, but I'm not sure if it is now (although qualified English teachers who can teach English with a sideline in special needs and 'English as a second or additional language' are always in demand), but I would imagine there are still jobs available, especially in London, although some of those jobs might be in schools that are a little "challenging".
2) I'm not sure about this one. I think your American qualification would be recognised as allowing you to teach, but only as what is called a non-qualified/temporary teacher. With that status, you can work for 4 years before you have to qualify or stop, but you don't get paid much with only that status and it can be harder to find a job. To become a qualified teacher you need to pass various assessments which you can do while you are working as a temporary teacher. Usually it takes a year of classroom teaching to pass those assessments, although you can fast-track through it if you have more experience. There's more info at:
3) The unqualified teacher's pay scale starts at approx £14,000 but individual schools can pay more at their discretion. The newly qualified teacher pay scale starts at around £19,000. If you work in London, you get a special allowance because the cost of living is so high, e.g. a newly qualified teacher would start on around £22,500. I think there are various bonuses and allowances too, depending on training, qualifications, experience, what subject you teach, etc.
Hope that helps & good luck!