I was in UK as a student between 2009-2011 and I finished my MSc in Business Management from warwick University.
Now I wanted to pursue my Masters in Information Systems (Full Time) from Staffordshire University.
I understand that both the masters are Level 7 courses from UKStudentsVisas for internationl.

So here my questions are,
1) can I do my second masters now from the same Level but different subject area & being an international student?
2) What is the minimum fee to be paid by an international student to get an Unconditional offer letter from the University?

1) Yes, I don't see why not, unless there's funding restrictions. There shouldn't be visa or uni restrictions on this.

2) Zero? I don't think you pay until just before you start