If this is to be a career change for you (and your age would suggest that it is a career you could pursue for a number of years), then I would go down the ATPL route.
If you do the CPL exams, get your CPL and FI rating and then subsequently decide that you need or want to get an Instrument Rating to extend your instructor potential you would need to do the IR exams. Two of my colleagues did the CPL exams only and regret it now as they both would like to to an IR but couldn't face the studying again.
Remember though that there is a time limit of 3 years from the end of the month of your last exam to have CPL and IR issued. The time limit does not apply to the FI rating.
Ref your other post on the Professional forum... Bristol Ground School is up there with the best of them.
Hope this helps.