So that avoids having to complete the ME/IR (if that's your intention) within 3 years of the final exam pass.
Feel free to correct if I'm wrong!
Yes you are wrong! The 3 year validity of the exams to obtain a CPL and an IR is totally seperate from the requirement to have demonstrated CPL knowledge, which once done is valid for entry to a FI course without time restriction. Having an FI rating does not freeze or have any influence on the validity of any exams you have taken.
To get paid for instruction you'll need a commercial licence (CPL) and a class 1 medical.
Under current rules, but after April 2012 you will be able to be remunerated for flight instruction as the holder of a PPL with an FI rating and a Class 2 medical.