I'm going to face punch you a bit even though you have things largely under control:
Pay off the credit cards. Even if they are on low/no interest deals making you technically better off carrying the balances, they're just stupid.
Sell the $45,000 fleet of automobiles and replace them with, at most, $10,000 of used car -- a 7-9 year old Accord, Prius or Ford Fusion, or an antique Volvo station wagon, are all good choices. Is your side-hustle driving for Uber? If not, you shouldn't be allowed to post on this forum while owning so much automobile.
Your grocery spending is absurd. The blog has a post from back in 2012 all about $1,000 monthly grocery bills and why they are silly. Come back when you've got this down to $600 month, including toiletries and cleaning supplies.
Random shopping of $535 per month? So important and necessary that you cannot remember what it's all for? The rules of the forum call for a miscellaneous category of 2.5% of monthly spending. Break up that line item until you're left with a truly miscellaneous grab bag worth $150, tops.
$664 on health insurance is a lot, but I'm guessing that's to do with your running your own business as opposed to taking advantage of a heavily subsidized employer plan. When budgeting for your next career move, look into whether an employer plan is in your future with a lower out of pocket cost. Maybe through your wife's job?
$485 for child care is kind of a drag, but it's only a for a few more years. Once the youngest is in kindergarten that should go down a bit (but you'll still need something for weekends, and then add back after school activities or summer camps when the kids get older -- still, if you are thoughtful, you can cut this in half or more when they start school).
Have you wife max out her 401k and get over the psychological issues. At your earnings level, the tax hit is substantial.
Start 529s for each of your kids and contribute heavily. Depending on where you live you might get a state income tax deduction for a few grand of contributions every year, which is nice.
Don't stint in your SEP IRA. Even if, 10 or 20 years from now your find yourself needing to tap that savings, you can explore SEPP withdrawals as a way of avoiding the 10% penalty. At worst, you can just eat the penalty -- chances are, you will be in a lower tax bracket when the time comes, given how high your bracket is now, so you'll still probably come out ahead. The tax hit at your current earning level is big.
You have small children, and live in a nice house near extended family. You're in it for the long haul. You spend a lot but save just as much, so fundamentally things are pointed in the right direction. Still, given the rate at which you burn cash, you'd need a pretty big nest egg in order to safely hang up your spurs.
Given your circumstances, the rough outline of the plan is this: Keep slaving away at the cash cow job until your house is paid off, you have $1 million in liquid investments (spread among taxable and retirement accounts), and each kid has $50,000 in a 529 educational account. That's probably another three or four years, or probably when the youngest goes to kindergarten (unless more are on the way?).
Then pull the trigger, making sure either you or your wife have access to a good, reasonably priced health plan through her job or your next business. Try to keep total salary income at least above $60,000 per year for a few more years after you make the jump. Will you be keeping unidentified side business #2? If so, everything is already lined up. If that goes away when you pull the trigger, I wouldn't worry too much: the hole you're trying to plug will be pretty small, and even though you won't want to rely at that point on your retirement savings to fill the gap left by your wife's salary, you can safely do so while waiting for the new venture to pan out.
