dnd 5th – Help me balance this subclass of bard

The bards of the storm college use the creative magic of thunder
and lighting. They bask in the beauty of the storm.

Skills bonus:

You gain mastery with medium armor.

Stormy blades:

When you join the College of Storm at the 3rd level, you
gain the ability to make your attacks with a weapon steeped in magic
thunderous energy.

Once per short rest when you hit a creature with an attack at the gun, you
You can choose to inflict 1d6 additional Lightning Damage to this target. This
damage increases when you reach certain levels in this class,
increasing to 2d6 at the 5th level, 4d6 at the 10th level and 7d6 at the 15th
level.

Bonus spells:

In addition, when you join this college at the third level.
You get the thaumaturgy cantrip and a spell of any class.
deals with lighting or thunder damage the spell must be of a level that you can
discard. When you choose this spell, it becomes a bard spell for you. Yes
you choose to replace this spell when you gain bard levels, you must
replace it with a spell that deals damage to light or thunder.

Additional attack:

At six levels, you can attack twice instead of once when
you take the attack action on your turn.

Fury of the storm:

From the 14th level, when you are hit by a melee
attack, you can use your reaction to inflict lightning damage to the
attacker. The damage is equal to your bard level. The attacker must
also make a force save roll against your bard save spell, save DC.
In case of failure of a backup, the attacker is pushed in a straight line up to 20
feet of you.

I think this subclass is unbalanced because of the number of skills acquired at the third level. And the combo moves that you can remove with stormy blades plus something like a thunderclap. But I'm not sure how to balance it while keeping the feeling of this subclass.