I have just gone through the painful (and expensive!) NZCPL conversion process,
You should check out how expensive it is to go the other way, i.e. NZ CPL to UK CPL, you might learn what expensive really is
What sort of credibility would you have (assuming you end up with a 'multi-crew' NZ MEIR) applying to some small companies operating single&multi engine aeroplanes (single pilot ops) in your opinion?
Have a think about what you have written. How would you view an applicant that applied for a single pilot MEIR job but that applicant was only two pilot (multi crew) qualified? Would you give them the job? I suspect probably not.
Either way you'll also have to do a competency check under the Check and Training requirements for who ever you work for.
You often hear it quoted that in country experience is either required or beneficial, I've never heard of anyone actually being told this though no doubt it may have happened. In cases where it has happened one might suspect that it was another way of saying don't call us we'll call you. I don't think recent in country experience is all that important.
Also think about how it may look if you take a convoluted route to converting your qualifications. The question may be privately asked, why did he/she do this? Was it to cut corners? Does it give a hint that he/she may be prepared to cut corners in other areas too?
Also your fATPL is pretty well worthless the exams will count for nothing, but I guess you already know this.
On thing that's not clear from your posts is whether you have a job or just getting organised to go job hunting. I'm guessing from your posts that you're going to be job hunting so a single pilot IR is what you probably need, otherwise a two pilot one may be quite satisfactory.