Oh I mixed it up with 3. Yes you don't need #4. I could still have 8.8.8.8 routed to me in v-next, and then later do something with 8.8.8.8.1, so it's 1:1 but not onto. Instead v6 did completely new /64s with random addrs inside, no association with the v4 addrs.
About the others being optional, no they aren't really, because most devices will implement the minimum. Android doesn't support dhcp6. My router is like most and has no option to enable dhcp6 or nat6 anyway.
Ipv6 spec also says that a router could either default allow in or not via its firewall. In reality it's usually default deny, but not always, hence the freakouts people have about security in v6. V4 spec doesn't know about NAT, but in real life the answer is no you don't get inbound connections or even a publicly routable address unless you deliberately configured that.