Hi,
You can import CDs to the music app. Import music from a computer to Music on Mac – Apple Support (UK). The music app is free and As long as you keep the music on your computer, you will be able to play the music. I suggest that you make a backup on an external drive.
If you subscribe to Apple Music, your music will either be matched with music in Apple servers or uploaded if not matched. The matched and uploaded version will be available on other devices.You existing library will not be changed unless you opt to remove downloads and stream from cloud. Matched music can be upgraded by removing download and re-downloading.AAC, Lossless and hi-res Music downloaded as part of your Apple Music subscription will only be available as long as you have an active subscription. Back up your own before subscribing.
Jim