For setting the resolution I usualy include a "video=1280x720" to the GRUB_CMDLINE_LINUX and will force the resolution I like both for the splash screen as well as the login screen. Then I leave grub menu itself in plain text mode GRUB_TERMINAL_OUTPUT="console".
Not all video drivers are well behaved, so plymouth needs to revert to text mode. I don't know for sure, but I would guess you would need to rebuild the initrd image after you built the nvidia driver. "dracut -f". Otherwise the video driver can't be loaded until long after plymouth has started.