Jacks,
Please don't misunderstand my sentiments - your background and experience will be recognised and most likely very well appreciated, not least by the more senior captains you will fly with. It's getting through the initial filtering that is often the greatest obstacle. Your plan and goals are well thought out and as airline flying in my view is not perhaps the be all and end all it once was, you are right to continue with your current career for all the benefits, experience and satisfaction it brings. I don't feel age will be against you frankly, if the market continues as it has been for the past 18 months (you will have observed how cyclical this industry is though), and as you say, in the unlikely event nothing comes of it, you will have had an interesting journey and be well qualified at the end of it. You mention possibly doing a bit of instructing which in all honesty, can be an extremely rewarding occupation both part or full-time (providing you won't be reliant on either a sustainable (with family) or necessarily consistent income as a PPL FI).
You identify the value in strengthening your training background through the use of one provider and that is important, as is the goal of coming out the end of this debt free. I would be cautious about MCC/JOC; ATO's that have a proven airline placement record are not necessarily the same as those that have a commercial agreement with an airline in terms of mentored or sponsored training programmes and I would be wary of using an integrated ATO for this having followed the modular path. Some ATO's simply don't know how to handle modular students despite being keen to take your money. There are others not on your list that have excellent reputations and I would research these as well as visit each before making a decision. Additionally, 8 years is a long time in aviation and training providers come and go as well as EASA's proposed changes to the MCC/JOC training framework which will most likely mean that MCC as it stands today will be part of a more comprehensive JOC/Evidence Based Training CRM module.
One last point, try to seek out as many ex-Army rotary (or other) airline pilots - there are some out there. Having a referee or an ex-mate that can give you a steer in the right direction when looking for that first job can be enormously helpful. Looks like you've done your homework so, again, best of luck.