Shawn pretty much has it answered but I just want to add a little bit Their meanings are indeed slightly different but they are also similar enough that they are interchangeable depending on the context of the situation. In Shawn's example 1 you could use 6,1,5 and maybe even 2, but never 4. In his second example you could use 1,2 and 4 but 3,4 and 6 would be weird. In ex. 3 you could use all of them, except 6.

No. They don't all mean the same thing. For instance, you would say 6 if someone said you weren't going to complete a task because of all these complications arising from your ability to manage it or if someone asked you about how a project was going. You would say 5 if you are offering to do something for someone even if they don't ask you to do it. For instance, if someone says "I need flowers brought to room 16 but I can't seem to find anyone who can help me." You would say 4 if someone asked you to do something and you are going to do it for them. For instance, "Can you have flowers brought to room number 47?" You would say 3 if someone tells you something that you should do. For instance, "He broke your window? You should make him buy you a new one." Number 2 is like 5. Number 1 is a response to someone asking you about the progress of some task or project.