one more thing to be careful about is partial rollover.
"
You cannot isolate your after-tax IRA money and convert it tax-free
while keeping your pre-tax IRA money in the Traditional IRA.
When a partial conversion is done, a pro-rated amount of after-tax money
(or basis) is included with each dollar converted.
For example, if you have IRAs worth $40,000 and $20,000 of
that money is after-tax, when you convert $20,000 of the Traditional
IRAs 50% ($10,000) will be tax-free and 50% ($10,000) will go towards
your taxable income.
"