You can buy a USB blu-ray drive for like $50.
You can buy a USB blu-ray drive for like $50.
Rather than build a computer, check out NAS devices.
My Synology NAS does everything you mention except ripping, and you can rip with any computer that has an optional drive.
A NAS is lower power than a tower server, and many are designed to let you swap hard drives.
Retroarch box for your TV?