a-wing,
Your plan sounds like a good one to me. I have a CPL/IR fATPL & MCC and shall shortly be commencing the FI course. When asking around you'll find that some schools are loathe to employ instructors who are looking to move onto the airlines ASAP because, rightly or wrongly, they assume the instructor will not be interested in teaching. Personally I see their attitude as rather ludicrious and arrogant really as I don't know any qualified pilot who would take such a cavalier attitude towards something so rewarding, however I guess some do otherwise this attitude would not exist!
Other schools are cool with aspiring airline pilots using them to gain experience and will actively encourage them towards achieving their ambition. As someone in this postition my attitude is that I'll put everything into instructing until the airline job comes along - no point in slacking when there is so much for me to gain in terms of job satisfaction! It is all about attitude and that's a two way thing in my view - if a school takes the attitude that an aspiring airline pilot is going to take a slack approach towards instructing without even judging each individual on their own merits then it points towards a prejudice which then poses the question: would you wish to work for a company who may view you with such contempt? Something to think about!
The only small downside to your plan, as I see it, is that you won't have the extra instrument experience which the IR provides to fall back on should you get caught out one day with poor visibility - but seeing as the majority of PPL aeroplanes are not certificated for more than PPL IMC conditions this is a very small issue in reality, and we all know a PPL should not find themselves in this position anyway but the experience and hours part may be a factor when they look at the overall picture. At the end of the day there are no hard and fast rules to getting a job in aviation - if you are qualified to instruct and they have bookings and not enough instructors on hand you'll get the gig unless someone more experienced is available. Worth doing all the training before the FI for this reason alone? My answer would be 'no'.
As Han 1st Solo said, most schools will be more welcoming towards someone who is not simply looking at instructor work purely as a stepping stone towards a career in the airlines so my last peice of advice would be to exercise caution in how you approach any potential employers!
Good luck,
VFE.