1) Yes, that is correct. But there are some timing requirements if you plan to do any QCDs to reduce taxes on your RMD. And if you plan to convert in an RMD year, you must complete your RMD prior to converting.
2) Yes, withholding from RMDs can usually replace the need to pay quarterly estimated taxes if your RMD is large enough in relation to the amount needed to be paid in to avoid underpayment penalties. One popular method is to take the bulk of your RMD later in the year when you have figured out the amount you need to withhold. A large advantage to withholding is that it is treated as paid equally throughout the year regardless of when you actually take your RMD. Estimates are only credited when they are actually paid. So you can hang on to your money longer when you pay by withholding later in the year. It is also a simpler and easier way to pay.