Daniel,
To clarify if you obtain a South African CPL/IR, then the conversion is as you stated, sit the 14 ATPL exams, to convert the CPL it is then training as required and the EASA skill test, then to convert an ICAO IR it will be a minimum of 15 hours training and the EASA IR test. I did note that you only mentioned CPL in your post, was your plan to do the CPL initially then do the IR at a later date? So that is all quite achievable. You are correct there is little point sitting the stand alone 9 EASA CPL exams as it gives no cross credit to the ATPL so it is best just to do the 14 ATPL exams from the start.
Regard to working as an instructor in Europe, we need information on your nationality (we can make assumptions based on your posting name) but unless you have EU or EEA nationality then I doubt you would get a work visa to work as an instructor (though again not impossible but more difficult without the nationality).
The other thing to be aware of is the current state of the Aviation industry. While there was an instructor shortage, I expect there will soon be a glut of instructors, as former instructors lose airline jobs there will be several looking to come back to instructing and alot of fresh qualifiers opting for instructor rating in absence of any other option.