From where you are now, with your experience behind you, it would certainly be worth doing groundschool, then straight into the FI rating. You could then start instructing weekends straight away - and get paid! You could then get the CPL and IR later on (assuming you want to go all the way if you're doing ATPL groundschool).
The only thing to watch out for if you are doing ATPL groundschool is that you have 3 years from the date of the last exam to complete both the CPL and IR and get the paperwork to the CAA.
I went CPL-FI then waited about 18 months before I did the IR, best decision I ever made as it got me onto the instructing scene much quicker with much less debt for the first year, and no IR revalidation to worry about. That was before you could get paid as a PPL-FI, and with your experience already there will be no problems with the 200 hours required for an FI course.