Q: 2019 is the first year I need to take a required minimum distribution (RMD). I have a total of three 401(k)s and an IRA. Do I need to withdraw from each account? And do I need to take all of the RMD at once?
You can choose whether to take your RMD as a series of smaller withdrawals throughout the year, or as a lump sum. Let's say that you're required to withdraw $24,000 this year. If it would be more convenient to set an automatic withdrawal of $2,000 per month, that's perfectly fine to do.
Second, your RMD is based on your total balance in your tax-deferred IRAs, but for 401(k)s, each account's RMD needs to be taken separately. In other words, the IRS doesn't care if you divide your RMD proportionally between all of your traditional IRA accounts or just pull it all from one IRA and a few 401(k)s, which is generally the easier way to go. However, if you have money in an IRA and a few 401(k)s, you'll need to calculate your RMD separately for each one.
Your RMD is based on your accounts' value as of Dec. 31 of the previous year and is calculated based on IRS life expectancy tables. As long as the required amount of money leaves your tax-deferred IRAs and each of your qualified retirement accounts by the end of the year, it doesn't matter which specific accounts you withdrew it from or how frequently you took distributions during the year.