That's a very difficult set of questions, and there's no simple solution. The modal verbs "have to, should, supposed to, must, need to" etc. can have very similar meanings.
Put simply (and generalising), if you "have got to" do something, you 'have to' do it (a variant of the first), and you 'must' do it. These all mean a strict obligation to do it. "What must I do?" = "What do I have to do?"
If you are "supposed to" do something, this carries less of an obligation. It means you 'should' do it, 'you 'ought to' do it.
"You are to do something" is even less clear.
But often the lines are blurred. And what one person thinks you 'must' do, another might think you merely 'should' do.
For example whether "You must obey the law" and "You should obey the law" is true, depends more upon your philosophy of life than grammar.
If you're still unclear, you could ask some specific questions with examples.
Yes, the position of 'please' is perfect.
Student or Learner