So I'm creating a subclass of Sorcerer to add all Necromancy spells to their spell list. Is there a way to do it where they don't have to pick one out of the list? I'm trying to get them all to add to the spell list without creating like 20 different features to add each one.

That depends, do you want them automatically known, or just learnable?

Automatically known, do I just add each spell as it's own, set it to Uses Spell Slot, Does Not Count as Known, and Always Prepared?

Quote from Hand_Cannon >>

Automatically known, do I just add each spell as it's own, set it to Uses Spell Slot, Does Not Count as Known, and Always Prepared?

 
Yup, but you can skip “always prepared” since sorcerers don’t prepare their spells.

Is there a way to hide it from the character sheet or will it always be there if it's added?

It will always be there.