CPL exams will only be enough for you to fly commercially, but VFR.
The IR exams then add the ability to fly IFR (you usually also add multi engine, but not always)
The ATPL exams then add the ability to operate commercially in a multi crew aircraft.
If you seriously know you will never ever operate multi crew, fair enough, but since the ATPL exams compared to both CPL and IR really isn't much extra, I don't see any reason not to just do the ATPL exams in the first place. If you get the IR and CPL and then at a later date decide you do need the multi crew ability, you'll have to go back and redo all the ATPL exams, recovering everything you've already done just to add a tiny fraction more.