Mnrtoler says:
I’m only reading stuff related to character creation. Do I need to read anything else?
TLDR on the whole thing could probably be summarized by two things: 1 Skills/Proficiencies are more important, and 2 Wisdom is important for Every. Single. Character.
More specifically...
AIME added several, basically, mini-games to 5E in an effort to make the game flow and "perform" in a more Tolkienian fashion.
These mini-games impact how you will likely be able to perform, mechanically, during adventures, and impact how long your PC may "live" (i.e. how long you get to play them for).
I am also, as mentioned in the recruitment thread, going to use a version of Skill Challenges. Probably pretty heavily. Another mini-game that does not flow like, and prioritizes different things than, vanilla D&D.
I would recommend at a minimum reading about the following two subjects from the Players Guide, as you cannot avoid participating in them:
The Journey Phase
The Shadow
As well as my rules for Skill Challenges in the OOC Resource Thread.
Some other things that you might want to know.
I forget which class you're pursuing off the top of my head, but Audiences are another mini-game that can be important to understand.
And the Fellowship Phase is new mini-game that replaces Downtime and can provide some really neat opportunities for character development, or they can be a complete waste of time.
Long Rests are different/harder to get.
Exhaustion is a big thing/very common Condition to get.
What else...
EDIT: HD are a resource used fir more things than just healing on Short Rests (all in all healing is harder).
Basically, if you care much about the game portion of the game, and being able to create a character that performs well mechanically in the things that are important in AIME, it would behoove you to understand how these new mini-games and other systems changes work.
If you're cool with taking game mechanics changes as they come, and won't complain when something you didn't know about causes you trouble?
Don't worry about it.