How to complete the third speedstar race

Skins are listed as Key Items. Once you've redeemed the preorder codes for the skins, they will appear in your Key Items and you can simply equip them from there.

From this guide:

First off, bring up the game’s main menu and head over to the Items tab. Look for the Key Items option and select that. Here, you’ll find all the important items you’ve picked up over the course of the game. Select the skin that you want to equip, and then hit the Equip option. Once you do this, your Pod will assume the appearance of whatever you picked for it.

As someone who also repeatedly died on the first level and had to replay it many times, I vividly remember this dialogue. A lot of the "significant" things won't really stand out until you've reached the true ending, so although I'm going to explain within spoiler tags, don't take them lightly.

1. Yes.

2. I honestly don't know exactly what is said, but from the bits I was able to pick up, it sounds like a mix of some prerecorded announcements and messages for the factory while it was still in use by humans before they left.

3. See spoilers below, but as I said before, this includes very important plot points, so proceed with caution...

The fact that 9S says that nothing machines say make any sense is a bit ironic after you discover that YoRHa androids' black boxes are repurposed machine lifeforms cores. That is to say, YoRHa androids are essentially just prettier machine lifeforms. The YoRHa androids only differ from machine lifeforms in that they were created by different things. The argument that they look different is disproven when the machine lifeforms create Adam and Eve. This line in particular isn't exactly significant story-wise (however, the idea that androids are superior or otherwise different from machine lifeforms is a recurring theme and you will see dialogue like this throughout the game), it is something that you will pick up on when you hear it again after completing the true ending and learning the truth about everything.

Another reason this is important is that is a subtle hint towards the fact that is revealed much later on that machine lifeforms were created with the purpose of "destroying their enemy," however, they eventually realized that without an enemy, their existence is meaningless. Thus, they will never fully destroy the androids. In an effort to ensure this, they allowed themselves to be created with imperfections and anomalies that would hinder their own attack power. Examples of these anomalies would be Pascal, the Forest King, and the machine lifeforms who express more human traits, such as speech.

As for what the Goliath machine lifeform said outside the facility, unless I missed something, I'm pretty sure that one only repeats "KILL... KILL... KILL..."

However, you will meet MUCH more articulate machine lifeforms later on.