Is anything I should check before I unlock my bootloader and void my warranty?

Backup all your files, unlocking the bootloader will wipe the device

You may lose the ability to view DRM content at high resolutions.

Back up your files, but I would also Double check your location / Providence laws regarding warrenties. like in the US I'm pretty sure, while the manufacturer May state that rooting your phone and unlocking the bootloader will void the warranty, this would be illegal under the Magnuson-Moss Warranty Act. Under this act a manufacturer of a consumer device while not obligated to provide a warranty for their product, if a warranty is provided must adhere under the restrictions of the act, in particular in the case that matters for this a manufacturer must not disregard a warranty for a modification to a consumer good unless there is evidence of proof that said modification is what caused the issue at hand.

For example if you unlock the bootloader of your phone and the speaker failed a few months later that's clearly a hardware failure that had nothing to do with the fact that you unlock the bootloader on your device so they would not be allowed to refuse your warranty based off. However if you somehow managed to fully brick the device by unlocking the bootloader and installing something wrong, that would be a clear you caused the issue by doing this modification which means they would be allowed to refuse warranty.

Please also note that this doesn't mean they can't refuse to help troubleshoot and provide tech support, the only thing they can't refuse is the actual warranty part of it