For people doing the roth, how do you decide how much to convert in year given the 5 year lag? The lower of 400% of the FPL (for ACA) or the top of the 15% tax bracket? Your budgeted ER expense?
It all depends on your specific tax situation, especially in retirement when RMD's kick in. Will you be in the 25% tax bracket then? Are you in a lower tax bracket now or during early retirement? If so, it would be beneficial to take advantage of the lower tax bracket to get some of the tIRA value out at a lower tax cost. If you don't need the tIRA income, you do it as a Roth conversion and preserve the tax advantages (as well as effectively adding the tax amount to your IRA value).
You can save taxes by Roth converting at a lower tax rate, but it might cost you an ACA subsidy, a tuition tax credit, a Roth IRA contribution, a boost into the 15% or 25% tax bracket, AMT taxes, or some other extra tax increase. That's what you have to look at for yourself.
In general, it will be beneficial to convert more earlier, even with a higher tax cost, and then ramp it down a bit later on. That's because you get more after-tax value in a Roth (no taxes on withdrawals), and the earlier you get your money in there and the longer it stays the more advantageous it is.
I my case, this means Roth converting up to the point where AMT taxes start to hit for the first seven years or so, then trimming back to the top of the 15% tax bracket until RMD's start. I'll pretty much be hitting the top of the 15% bracket throughout retirement, using tIRA withdrawals to hit the top and Roth withdrawals to meet the rest of our income needs.