There are some minor hardware differences depending on when you bought your deck and random chance. If you buy a brand new deck for example you may find you have a different heat shield than in most of the older tutorial videos for the deck.

Another example of differences is that two different styles of thumbstick were used, and until recently you were limited in what replacement thumbstick upgrades would work depending on which type you had (now they have universal upgrades that work with both kinds).

The only thing you'd be missing is the anti-glare screen that comes with the top model.

Yes.

I bought the lowest level Steam Deck, cracked it open before I even turned it on. Replaced it with a 1TB Sabrent drive. Couldn't be happier.

theres a screen replacement that can be done. but personally id rather have an oled 720p screen at 7" than a higher resolution one. the deck is pushing its limits as it is and adding more resolution will hurt that more than anything. or maybe im wrong idk.

This is the way to go. Personally I prefer the glossy screen over the matte anyway.

I believe valve suggests not changing the ssd, voids the warranty and all that as well. For me I just got a proper sd card with good stats (A2, class 10, etc.)

That said, I feel like they should be swappable if you were to get your hands on one of the bigger ssds