Okay, three fixes:
- EB invocations only affect one beam.
- Devil's Sight does not work on magical darkness until level 7.
- Hexblade's Hex Warrior requires 3rd level.
Then give Warlock standard spell progression, except they lose 1 spell slot at each level (to a minimum of 1 spell of that level). Then create these Invocations:
Expanded Warlock Magic I
Requires level 4, ability to cast 2nd level warlock spells
When you select this invocation, you gain additional spell slots,. You gain one 1st level spell slot and one 2nd level spell slot.
Expanded Warlock Magic II
Requires level 8, ability to cast 4th level warlock spells, Expanded Warlock Magic I
When you select this invocation, you gain additional spell slots. You gain one 3rd level spell slot and one 4th level spell slot.
Expanded Warlock Magic III
Requires level 10, ability to cast 5th level warlock spells, Expanded Warlock Magic I, Expanded Warlock Magic II
When you select this invocation, you gain an additional spell slot. You gain one 5th level spell slot.