You headed this up PIFR vs CIR. No-one seems to have answered that. If you intend to fly privately (only) PIFR has the big advantage that you can just do the FPA's that you need/want - tailor it to your needs. You may not need ILS, if so dont do it. You don't need a CIR for private flying - PIFR does the job. If you intend to go to CPL, go CIR (but as already said get the PIFR endoresement in the log book as well - it might get you home sometime when your CIR is not current).
As far a recency goes under PIFR, the CASA requirement for a two yearly AFR is a bit slack. Many places mandate the CAO 40.2.1 recency requirements and I agree with that.
For the theory, it's a good idea to do IREX as it will cover you for all FPA's under PIFR.
PS - I did PIFR in a single.