All seems quite sensible, however do note your from finishing the ATPL exams you will have 36 months to get the CPL done, as the CPL is only 25 hours of training best to get the CPL out the way earlier than you do in your plan. Plus with the CPL you will need 50 less hours to do the FI(R) than if doing it on a PPL.
Also with the Competency based IR you can upgrade the IR to a full IR. Don't get too wound up about trying to achieve 90 percent average in the ATPL exams, there are probably only about 2 Airlines that have such a requirement and for the sort of roles you are aiming for no one is going to ask or care that much.
Multi engine hour building, you will need 30 hours p1 multi to do the MEI upgrade once you get you FI restriction removed.
Just for reference PPL level instructional pay is around 20 to 30 pounds per hour flown. So with part time PPL level instructing don't expect to make much back.
Working for an integrated school SEP Instructor salaries are now around 35- 40k per yea (with bonus's over 40 is possible). Multi instructors are getting salaries around the 50 to 65k mark.
However it is expected there may well be a surge of instructors in the next year as fresh qualifiers look to do FI ratings and many former instructors laid off from the Airlines return to instructing. So SEP pay rates may decline again. There however does tend to always be a shortage of multi engine instructors.
Also note to be able to teach IR you will need to get 200 hours IFR; you can do the IRI add on to the FI rating and be initially restricted to teaching the IRR only and then use the IRR instructing to build the IFR time.