Get thee a tax attorney.
...you don’t need the attorney ..yet. Find a tax preparer who is an Enrolled Agent who has IRS experience. They have been on the other side of the desk and will do the filing and know how to negotiate with the IRS.
The tax attorney may bleed you dry and is in no hurry to complete things if the clock runs...
Get your numbers together and get one year at a time done and if there are penalties, at least the interest rate is low. Good luck.
ymmv
I concur with your advice. I would also recommend getting your records as organized as possible, by year.