As I understand it, after 59.5 years, any Roth IRA withdrawals incur no tax, provided the account is at least 5 years old. Therefore, if my only income after that age were from Roth IRA withdrawals, I would pay no income tax.
After that age, if I had additional income that was taxable, could the rate at which the additional income is taxed be affected by the amount I withdraw from the more-than-five-year-old Roth IRA that year?
From the IRS:
You do not include in your gross income qualified distributions or distributions that are a return of your regular contributions from your Roth IRA(s).
It's not just that the particular money you take from the IRA isn't taxable. It's not counted as part of your income at all, so it won't have any effect on the taxation of other income.
The answer to your first question is true. No tax on withdrawls. Under these circumstances, the withdrawl is "qualified".
To your second question, as long as the withdrawl is qualified, it is not taxed, regardless of your additional income.
http://www.investopedia.com/articles/retirement/03/030403.asp?lgl=rira-baseline-vertical has a very comprehensive, plain English, description of the IRS rules (as of today, anyway).
