Doesnt have a dashboard per-se for centralized administration. It has a web ui to manually create create/upload collections. I personally use it a very simplistic way and just reupload an updated .vcf file with all my contacts from time to time.
About user management, I dont know how you installed radicale but they have this docs https://radicale.org/v3.html#authentication












Self sign doesn’t defeat the purpose, you can add your own keys to your bios that you use to sign your kernel. I do that and have a secure booted Arch Linux installed.