Okay, will try to answer to the best of my knowledge.
1) All age groups give great job satisfaction but it depends on what you like. Are you willing to cope with bolshy teenagers? I'm an 11-18 teacher and love it, despite the challenges. Primary is a different matter - you have to help them a lot more and they can be more needy, but some people like this. I have done a little primary teaching and have friends who wouldn't do anything else.
2) My workload greatly depends on the time of year. Sometimes I hardly bring any work home, other times I can have 2-3 hours 4-5 times a week or a long Sunday session. The first year is very tough, but after that things get a little easier as you build up your own lesson plans, resources and tactics for dealing with more difficult areas. Primary teachers have a very different structure to their day, often having the same class with no free periods all day. Secondary teachers have some designated non contact time and see anything between 6-15 different classes per week (estimate!)
3) The students depend on the area you teach in. The pressure is the same at any school - more academic schools have a lot of pressure on getting results, less academic schools have more pressure on the classroom management side of things. Generally speaking, you have to always be firm, set boundaries, be human, have a sense of humour, talk on their wavelength, and bend the rules when necessary. There is no black and white. Get them on side and interested and the discipline more or less takes care of itself.
On bad days it's awful, but when it's good, you can't believe they pay you to do it.
any more questions, I'd be pleased to help