I'm confused -
My primary objective is to obtain a stand-alone (i.e. not "on the basis of") FAA PPL & ME Instrument, as i undertake most of my flying in the USA nowadays (Europe is so expensive).
The one country the FAA will do a license conversion with is Canada. Since you hold a private MEL TC license the FAA will issue you a regular PVT certificate MEL with some paper shuffling from TC, getting at least a third class medical (the only time I can think of when the FAA requires a medical and you're not in an aircraft) and pass a special 30 question Canadian pilot written test. Since it doesn't look like you have an instrument rating on your TC license you would then have to pass the instrument written and complete a course of training for the checkride to add INSTRUMENT AIRPLANE to your certificate.
But then you say -
(iii) Undertake and complete training for a Part 61 Multi-Engine Commercial Pilot Course, leading to an FAA CPL
For that your plan is basically correct. You'll need to withstand a TSA background check, have your CAA confirm your license status to the FAA, as BanjoDrone points out get at least a third class medical. (Your EASA medical is pretty much irrelevant at this point. I think you could take the instrument checkride on your 61.75 certificate with the EASA medical but you'll need the FAA medical for the commercial ride and you don't want to confuse the issue anymore than necessary.) Pass the regular instrument rating written (don't do the Foreign Pilot one, it won't transfer) and complete training for the instrument checkride and pass the checkride. Your 61.75 certificate will then be reissued with INSTRUMENT AIRPLANE - US TEST PASSED. Then pass the commercial written, train and pass the commercial checkride and you'll have a regular FAA certificate and INSTRUMENT AIRPLANE will be added.