You aren’t going to get Comcast to give you a permanent or static address assignment. They don’t do that. Everything is automatic through DHCP. Their system will give you a single Ipv4 address for your router to nat your hosts behind, and because ipv6 nat isn’t widely available yet, one ipv6 address for your router and one /64 subnet for hosts behind your router to use,
If you want inbound connections to get to you, you’ll have to automatically update your own A and AAAA dns records when the addresses are assigned or changed. My experience is that they let systems renew the addresses in perpetuity. Mine regularly goes months without address changes.
I was a network engineer by trade, and I’ll say its not the easiest thing in the world to set up self hosting on Comcast, even for a pro. However, it can be done, and it works great once it is going! Very solid, very fast connections, with great uptime. But… if you want paid support from your ISP, you’re probably better off looking elsewhere for hosting.