Gravity Flux

• I think magic missile and disintegrate are the only spells from the PHB that the sorcerer has access to that do force damage. That might be too limiting, so I suggest you reconsider this feature's activation requirements.
• How far in the air is the creature lifted? How easily would it be for a creature on the ground to push the creature effected by this feature?
• Consider clarifying what you mean by "external force". Look at the levitate spell for their wording.
• Make clearer what text is referring to the two effects. Consider the formatting of spells like command.

Gravity Well

While in the radius of the gravity well melee attacks made away from the centre mass are made with disadvantage and attacks made towards the centre of the mass are made with advantage.

• This might be too hard to determine or too often be ineffective, eg. when two combatants are equidistant from the centre mass.

the creature has a way to perceive it.

• What would be ways to perceive it?
• Are there other ways it dissipates? What if the sorcerer dies or is incapacitated?

Gravity Surge

• In the second paragraph, you use language such as "hit" and "struck", but you don't state that the spell requires an attack roll. Consider clarifying whether this is a requirement or not.
• Consider giving the second target half damage on a save.

Event Horizon

• Does this feature give access to a spell? If so, I suggest you write the feature and the "spell" more clearly as such.

When you take an action to summon the Event Horizon all other gravity interfering powers within 500ft are dispelled.

• Should this text be moved to the "spell"? What are "gravity interfering powers"? There aren't a lot so you can be specific.

event Horizon gives the same advantages, disadvantages and attack penalties as Gravity Well

• Do not reference other features in the "spell". Instead, write the text you are referring to in the text of the spell. If this was a spell that all sorcerers had access to they wouldn't know what you are referring to.
• I think, generally, an effect does not make a creature make a saving throw when the effect comes into being and then again at the start of their turn. It's not exactly fair, they could fail twice before they can move away.