The TurboTax W-4 calculator would be an excellent resource to use. https://turbotax.intuit.com/tax-tools/calculators/w4/
By answering the questions correctly you will be able to determine what you need to enter on the W-4 along with what adjustments you could make. When it comes to the income from RSU vesting, this is vest figured by keeping records of the amounts that vested and their worth. In most cases a form is sent out with this information to the employee. You can use this information to adjust your W-4 as needed as your income goes up based on the vested RSU's. If you elected to sell stocks to cover the cost of taxes, keep that in mind as well.
You can also consult with the brokerage for advise on how to handle RSU's.
