KIR@GCM as explained on http://www.qatarairways.com/Privileg...nts%20new.page you need to earn 540 Qpoints in one year or 1080 Qpoints in two years to retain Platinum.
Your questions are almost all answered on the QR PrivilegeClub webpages. Please read those and you will find the answers there and in an easily understandable and official form. The rules change frequently and it is very difficult to follow all the small rule changes that are required.