Unfortunately most ISP's in my area don't dish out IPv6 addresses without ridiculous monthly charges. I hope one day it becomes more commonplace.
If you've got an IPv4 address that responds to ICMP, HE's https://tunnelbroker.net/ offers free IPv6 ranges (a bunch of /64s and a /48) for free. You can configure a tunnel to work through many routers, but with some setup you could also have something like a Raspberry Pi announce itself as an IPv6 router.
Sites like Netflix treat HE tunnels as VPNs, though, so if you run into weird playback errors, consider configuring your device's DNS server/network not to use IPv6 for that.
As for your questions:
> how you do this
Open port 8888 to (prefix):abcd:ef01:2345:56, or whatever IP your device obtains, in your firewall. It's the same process as with IPv4, except you can use the same port on multiple devices.
> And how do you prevent someone spamming your devices or is the risk so low you don't care?
While some services have started scanning IPv6, a home network from a semi-competent ISP will contain _at least_ 2^64 IPv6 addresses. Scanning the entire IPv6 network is unfeasible for most automated scanners.
That's the job of a firewall and is unchanged between ipv4 and IPv6. Theyre both equally vulnerable to denial of service attacks
What do you mean by spamming? People are scanning the Internet the whole time to see what's there, and it isn't a threat unless you are doing something terribly insecure. Scanning IPv6 is impossible in practice anyway, due to the high number of available addresses.