It's all very simple!
You have 36 months from the last ATPL exam pass to get BOTH CPL & IR.
If you do not get one of the above, the exams expire. If you have a CPL at this point you keep it, if not you have nothing. If you then wanted to complete training for CPL&IR you would need to retake all 14 exams.
If you get the CPL&IR within the 36 months, you can then let the IR expire for up to 7 years. If it is still expired after 7 years, you would then need to retake all 14 exams to get your IR back. Renewing an IR is the same as revalidation, a simple flight test which is never as difficult as the initial, so one of these every 7 years wouldn't be too bad, and ultimately you should have a job in 7 years or just give up all together.
If you only want a CPL, you can do just CPL exams (I have no idea, maybe 9 exams?). If you only want an IR you can do only IR exams (again, no idea, 7-9 exams?). If you want both you could do both sets, or do ATPL exams. ATPL exams are the foundation of an Airline Transport Pilot Licence, which you will need to work in a multi-crew environment. If you are only ever going to fly single crew, no need for ATPL exams.
The MCC doesn't come into any of the above requirements, but it is required before you do a multi-crew type rating.