Yes, that's correct, you can make estimates if (when) he has self-employment activities, and payroll withholding should cover his W-2 income (verify he completes a W-4 with his employer).
You'll ensure there will be no penalties incurred by paying in 100% of the 2024 tax in 2025, so if you want peace of mind, you can make the estimates. Otherwise, if tax due for 2025 is over $1,000, you'll need to have paid in 90% of the tax due.
See: Form 1040-ES
