RFC 6164, Using 127-Bit IPv6 Prefixes on Inter-Router Links explains that /127 networks are good for point-to-point links:
On inter-router point-to-point links, it is useful, for security and
other reasons, to use 127-bit IPv6 prefixes. Such a practice parallels
the use of 31-bit prefixes in IPv4. This document specifies the
motivation for, and ...
You seem to be confusing the congestion window with the receive window. The congestion window is always >=1. The receive window can be 0. The congestion window is controlled and only known by the sender, and the receive window is controlled by the receiver and transmitted to the sender. They are two completely different things.
The receive window is ...
I have it set up where I have a 64KB memory space so fragments can
arrive in any order.
A 64K buffer is actually a mistake because it leads to a particular fragment attack where the bad guys can send packets that add up to more than 64K, causing a buffer overflow.
Is it a requirement for clients of any type to send the fragments in
sequential order from ...
Note that the "most recent version" you linked to is just a draft with no real implication.
RFC 793 doesn't actually specify this - early RFCs were like that and left much room for optimization. The timer variant is specific to a given implementation. However, we can safely assume that most implementations use your option A - a single, socket-...