JB,
One thing to consider if you do choose the FI route to build hours, having only a CPL, is the expense of the ME/IR and then an MCC. As a FI you will earn barely enough to live, let alone to pay for your additional ratings.
If I was you the 1st thing I would do before anything else is to get a class 1 medical. Once you have that, then do the ATPL studies prior to carrying out any CPL/FI training. The ATPL exams are valid for 3 years after that date of your final exam pass by which time you must have built up sufficient time for your ATPL to become unfrozen. And for your ATPL to become unfrozen, you need a valid IR and ME Rating. Sound confusing? It does to me too!!!
In short I would advise
1. Class 1 medical
2. ATPL theory exams
3. Hour building
4. CPL
5. IR/ME
6. MCC
7. Job hunting
I would try and complete points 1 to 7 in as short a time frame as possible because the industry has a lot of movement going on at the moment and is forecast to expand, creating more jobs for pilots.
Whatever you decide, good luck. I've recently completed all of the above training, so I'm "current". PM me if you need more info.
DMK