...my understanding is that doing 401k conversions and drawing the contributions (but not gains) I can access these post-tax dollars before 59.5 without any penalties. I think that Roth money is not considered income; would selectively drawing from that give my family a low income and qualify for really cheap insurance?
The Roth withdrawal would not be considered federal income, but the Traditional 401(k) to Roth IRA conversion would be considered federal income. It's not unreasonable to account for 5 years' inflation in your conversion, so in this case your income would be higher than your spending. At 2%, 5 year's inflation increases your spending by 10%.
If you skip the conversion to have really low income one year, you'll need a plan for where to draw income 5 years from now.
What about post-tax brokerage accounts, would spending dividends/sales from those also not count towards income? Thanks!
In these types of accounts, your dividends get immediately taxed in the year they hit your account and count as income in that year whether you spend them or reinvest them. I would say "why not send the straight to your spending account?" Sales are different. Here your income is only the gain. If you have $20K in stock that you purchased for $10K, you can sell all of it, spend $20K that year, and only show $10K of income.
By the way, I say federal income in the first part because Pennsylvania state does weird things with IRAs. Opposite of the feds they consider the conversion to be a non taxable event, but the withdrawal a taxable event.