Ok..I wasn't going to say anything and just keep my big mouth shut....Butttt,
Like many here I started flying at the age of 16 and now at the grant old age of 52 (30 yrs of combined airline flying) I'm nearing the end of the road you're just beginning. I've been active in aviation since the days of cheap avgas and rental rates and before computer desktops and virtual flying software were commonplace. You had two routes to the airlines back then, military and civilian FBO's and commuter flying to build time toward the big leagues. Back then you had to have 1500tt just to get the commuter airlines to even look at a resume and now it looks with the new rules it'll soon be a requirement. In my day that was just to fly right seat in a BE99 or Bandit. Times change and we all have to change with them. Needs of the airlines and the Omni-present/all knowing government dictate was is currently required. What was required 30 yrs ago is different today and will be different in the future. That, you can count on. Not necessarily better or worse...just different.
I been extremely lucky throughout my career! I say lucky because my preparation and hard work always seemed to be met with great timing in the industry on each rung of the career ladder. I've come to believe that "luck" and "timing" are the big "X" factors in aviation. Sometimes I couldn't believe how lucky I was and have been and contribute my good fortune to a much higher power that is out of my control. I've known and witnessed countless scores of folks just as qualified and more deserving than I fall by the wayside simply due to timing and luck. There seems to be no guarantees other than constant change in aviation and the ability to play musical chairs.
I've watched the continued erosion of aviation and specifically airline flying over the last 30 yrs too. Airlines, all employees including pilots have been asked to do more with less, take contract concessions, accept a reduced quality of life and increased dangers such as terrorism attacks and lithium battery fires (Doug Lampe, 744 Capt of UPS 6 was a friend of mine...they don't come any better or sharper!) that weren't even on my radar scope when I started. I've watched the continual downfall of common courtesy for one another in society and also respect for authority as we cocoon ourselves with our pretend friends on Facebook and Tweeter accounts while being impatient and ignoring real people we meet day to day. You never no how that person you meet today and interact with may affect your future...six degrees of separation and all that.
Back to the OP's post...
You are getting ready to incur huge debt (unless you're independently wealthy, oil tycoon or a trust fund baby) at the expense of your wife and 6 kids with absolutely ZERO guarantees of success or even breaking even for that matter and time really isn't on your side anymore. I can't blame you for wanting change, to follow your heart or try something new but understand that aviation is a very expensive crap shoot at best. There are so many pitfalls along the way you may not have considered including loss of your medical, FAA violations, economic downturns, furloughs, bankruptcy, etc. that are totally out of your control but you need to be aware of and consider.
Congrats, btw, on passing your first FAA medical. I've had two a year since I was 16. By the time I was your age I had accumulated 42 of them. That's 42 chances of knocking me out of the cockpit and each one is a 50/50 chance of failing. So far, other than a small dose BP med I've been good to go. No guarantees of that continuing and they get harder as you get older. So many things will knock you out of the cockpit for good that wouldn't even be a small bump in the road with a desk job. Just the price of admission.
You say you'll flt instruct at ATP when you're done with your ratings to build time? That's great! What if you don't succeed in obtaining your ratings? What if you can't or don't pass your CFI? It's not a given. Flying isn't for everyone and while desire is very important it's not the deciding factor. Many rookie NFL payers don't make the roster and it's not due to lack of desire. Ability, coordination, task management, the ability to quickly and accurately work through a complex problem while under stress are all important traits along the way to success.
What if when that time comes they don't offer you a position or don't have one to even offer you or due to economic times the student population dries up? What then? Backup plan? Also, not many people can afford to drop the kind of coin on ratings on a questionable future flying career anymore and I don't see many kids looking toward the skies like they did in the past. Even my own daughter and her friends poo poo the idea of flying for a livin'......it's boring they say. I was once that starry eyed kid that breathed, ate, slept and read all things aviation. I flew every chance I got and loved every minute of it. Now, unfortunately, it's a paycheck, a job and a means toward retirement and be able to do other things I love.
I could write a book on the subject but you're a big boy and I'm sure you've seen many of life's ups and downs by now. But if you think that aviation is all rainbows and unicorns and that it has to be better than what you're currently doing......be careful what you ask for. I know this post has mostly come across as cynical. It wasn't my intent but it's the truth has I have seen it over the years. You have a big decision to make and you have 7 other people to think about and who are counting on you to get it right. If you were mid 20's and/or no kids I say knock yourself out..go for it. With that many dependents I'm not sure I'd spend the exorbitant amount of money you'll be required to pay up front just to play. There are no easy answers but I can tell you it's not as simple as step 1, step 2 and then step 3 and I've made it. Aviation is a fickle thing.
Above all else, I wish you nothing but good luck and a safe, happy road to your dreams.