Marvel 1964 Overview

Firsts

First Captain America vs Iron Man fight

We get our first face turn with Crimson Dynamo, and they start telegraphing Hawkeye, Quicksilver, and Scarlet Witch's face turn next year.

Our first faked death with Tony Stark, and our first scheduling snafu as this death is announced in Avengers a month before it happens in Tales of Suspense.

Copied plotlines

Both Mr. Fantastic and Spider-Man get sick within a month of each other - not part of a plot, just a regular flu, used only for dramatic purposes

In the same month, Cobra & Mr. Hyde and Dr. Strange use a technique to follow an image and trace it back to a location.

In the same month Mr Fantastic and Giant Man planned to propose & chicken out - Foggy does the same later in the year.

Giant-Man/Wasp and Spider-Man are both lured into a fake movie like the Fantastic Four was.

Secret Identities 

Asgardians in general know about Thor's alter ego as Don Blake.

Giant-Man's identity is discovered, but not for long thanks to Hank Pym's ethically questionable ability to mind wipe.

Bruce Banner is called "Bob" by mistake in FF 25, which eventually led to a string of multiple middle names

Limbo

Loki uses it to hold prisoners, and Immortus travels in and out of it, but there is no unified field theory on it yet

Misc

I always thought the emphasis on Namor being a mutant was a 90s phenomena, but he and Thor both refer to Namor as a mutie.

The X-Man have a working relationship, to the point they can call each other.

We get two Beverly Hillbillies references (Aunt May and Ben Grimm).