IPv6: Why not use /126 on P2P links for IPv6

Answers to your questions:

1. No, just because device supports IPv6 it doesn't mean it support IPv4<>IPv6 transition mechanisms - they're not part of IPv6 protocol specification. So, it may support translating traffic from IPv4 to IPv6 and vice versa but it needs to support mechansism like NAT64.

2. Nodes communicate with the protocol of their choice, depending on the higher layer calls. If your browser points to a name, and the name resolves to IPv4 only, IPv4 will be called in to service it. If it resolves to both IPv6 and IPv4, IPv6 should take precedence, but a lot was done in recent years to make both calls simultaneusly and check which one is faster.

3. You need to have node that is dual-stacked, so supports both IPv4 and IPv6 or have support of translating between protocols somewhere along the way. If your router supports it - fine, if your ISP supports it - it's also fine.

4. You should see IPv6 as it should take precedence. If not, your IPv6 connectivity, at least to this specific site is broken. If you can use only IPv6 (you are not dual stacked) you can only reach around 4-5k prefixes around the internet, which is very small percent (out of 500k for IPv4). Normally, hosts are dual-stacked however, so you should be fine - using IPv6 for IPv6-enabled services, and IPv4 for all the rest.

5. That depends on the type of the service your ISP provides. You may have private IPv4 assigned to your internet interface, and it gets translated somewhere at the ISP edge. You may have public IPv4.

6. For SSL/TLS you're using names, not IPs directly. You should be fine.

7. Yes, while there are still works to provide NAT services for IPv6, general idea about IPv6 was to stop doing NAT, and provide global connectivity. It means that with IPv6 assignment, your entire internal network may be directly reachable from other parts of the internet, if you're using IPv6 addresses from the Global Unicast space. For IPv6 you can use other types, like for example Link Local only, which would provide internal connectivity, but block ability to access from remote locations. Generally, you should filter the traffic at the edge of your network if you don't want the internet to access your resources/nodes.

8. Unfortunately, I don't understand the question. Cloud services are usually OK with IPv6, Amazon at least is.

9. Start from here: http://test-ipv6.com/

IPv4 classes A, B and C have been deprecated since the publication of RFC 1519 in 1993.

I agree with you that 64 bits for host addresses is more than anybody will ever need, but that is how it is designed and never having to worry about subnet sizes is wonderful! :)