You get points from purchasing it, but they can’t be used to buy games. They’re just cosmetic, you can buy avatars, backgrounds, avatar frames, emoticons, etc. Anything in the points shop.
You can also claim a profile bundle, and if you get the 1TB there’s also an exclusive startup movie and keyboard theme. Make sure when you get the Steam Deck you log into the account you want to claim those on as you can only claim them once. (You claim it when you have the Steam Deck in your hands, it shouldn’t matter which account purchases it).
You’ll have to transfer either using an external HDD / SSD via USB-C, or you can transfer wirelessly using something like Syncthing or KDE Connect.