I'd say get the IR done before the FIC for the following 3 reasons i did:
1) You never know when you're going to be offered a job out the blue one day on an airfield and the chances of you getting hired if you need to explain that you need 2-3 months to do an IR first are not going to help.
2) You are already eating into the 3 years after your last ATPL exam to get a CPL/IR.
3) On an instructor's wages it's going to be hard to save or get finance for an IR, you will need to give up work and go without a wage for a few months for the IR into the bargain.