I had this idea for a Monk subclass. I don't know anything about balancing, so, please tell me what you think of it. If it is good, or if it could be buffed/ nerfed in any way!

Monastic Tradition: Way of Thunder: Monks who follow this Monastic tradition learn to use their movement to manipulate the air around them. Their Martial Arts is accompanied by waves of pressure that enhance both their defensive and offensive abilities.

Bonus Proficiencies: At level 3, you gain proficiency in the Performance skill, if you don’t have it already, as your movements become more akin to a dance. You also gain resistance to thunder damage.

Thunder Fist: At level 3, attacks with your Martial arts are amplified by waves of sonic pressure you create with your movements. You can make all of your attacks, be they unarmed or with your monk weapons, deal thunder damage instead of their original non- magical damage. In addition, you get to add your proficiency bonus to your damage calculation.

Pressure Augment: At level 3, you learn to channel your Ki into your movements and enhance the effects of your thunder fist. Whenever you hit a creature with an attack and deal thunder damage, you can choose to spend 1 Ki point to gain one of the following effects: 1) The creature is pushed 15ft away from you, as you use sonic pressure to force it back. This distance increases to 30ft at level 11 and 45ft at level 17;  2)The creature had disadvantage on attack rolls and ability checks until your next turn, as you disorient it with sonic pressure. At level 11 the creature can no longer use their reaction until your next turn, and at level 17, they also cannot take any movement;  3)The creature is encased in a field of sonic energy, and will take 1d8 thunder damage if it moves or attacks in any way until the start of your next turn. This damage increases to 2D8 at level 11, and 3D8 at level 17

Flying Fist: At level 6, you learn to propel your attacks forward. You can make an unarmed strike against any creature you can see within 30ft of you. The force of your attack is transmitted through the air and hits the creature as if it was standing right in front of you. Attacking in this manner does not allow you to add your proficiency bonus to your damage calculation any longer. The radius of your ranged hits increases to 60ft at lv 11, and 90ft at lv 17. You can choose to spend a Ki point to enhance your current radius of attack by 30ft.

Dance of Thunder: At level 11, you have built enough stamina from your training that you can keep in constant movement. Creatures have disadvantage on checks to grapple you, push you away, or knock you prone. As a bonus action, you can spend 1 Ki point to enter a dance until the beginning of your next turn. Any creature that comes within 5ft of you during that time takes 1D8 thunder damage. This damage increases to 2D8 at level 14, and 3D8 at level 17.

Warrior of Thunder: At level 17, you have perfected your techniques of air manipulation during combat. You can apply your Flying Fist feature to attacks with any of your monk weapons that are not ranged weapons. You now also get to add back your proficiency bonus to your Flying Fist attacks.

I quite like it, though you are adding features from existing subclasses earlier or without cost, not that it's bad, but I'd make a few changes:

1. Thunder Fist: thunder damage type is fine, but adding PB as damage is a bit over the top, especially since you don't need any activation, it has no duration and no ki cost (look at hexblade's curse for reference). Considering action economy is important for a monk, you could add a 1 minute-duration that triggers at the start of your turn for 1 ki (no action required).
2. Pressure Augment: it mixes Open Hand's Technique (Push with no save and a late Addle), Mercy's Physician's Touch (even better, since you can use this earlier and you don't have problems with enemies inmune to poison/poisoned condition). I would use the 3rd option as a whole feature (or as and add-on to Thunder Fist, so as to not increase the ki cost), since it is fairly strong as it is, I would change just a few things:
   1. Change the damage to 1 MA die and then increase it to 2 MA at 11 and 3 MA at 17.
   2. Add a little 5ft push or an attack of opportunity seal on the enemy for the turn.
3. Flying Fist: This one is fine, but if you end up adding a cost to Thunder Fist, then PB should be added to damage.
4. Dance of Thunder: The first half is ok, but the second half has no sinergy with Flying Fist, I would change it so that while your Thunder Fist is active, when you enter a space within 5ft of an enemy creature, they take 2 MA thunder damage (increased to 3 MA at 17).
5. Warrior of Thunder: Underwhelming, by level 17, your unarmed strikes are better than most monk weapons, except magic weapons (and you shouldn't account for those when making a monk subclass), if anything, you could make it so that the bonus damage from Thunder Fist is doubled

Be very, very careful about creating subclass features that are just better versions of existing subclass features. Pressure Augment is basically a better version of Way of the Open Hand's 3rd-level feature: yours is slightly more Ki-intensive, but it's stronger, more flexible, and doesn't give the target a chance to save. Flying Fist is a straight upgrade to the Way of the Sun Soul's 3rd-level ability; sure, Radiant Sun Bolt uses the less-resisted Radiant damage type, but your version allows the user to choose between Thunder or Bludgeoning, and the range increases automatically as you level, AND you can increase the range further with a small Ki investment. One of these two features might be okay on a subclass that is otherwise more restrained in its power budget, but probably not both.

Your other features are also remarkably strong. Adding proficiency to all attack damage by itself makes this subclass one of the best damage dealers in the game, and the no-save Thunder damage from Pressure Augment's 3rd option and Dance of Thunder just compound that. But this monk isn't just a phenomenal damage dealer; they're also among the strongest battlefield controllers, and they resist grapples, pushes, and knockdowns, which are some of the most common counters to high-mobility characters.

I think you need to look at one thing you want this subclass to be good at, and focus on that. Right now what you have is a vaguely Thunder-themed Monk that combines the best features from multiple other subclasses into a single, overwhelming grab bag.

One thing I do when I make a subclass is list out all the thematic things I want the class to do. Then I make brutal cuts, because there are always more ideas than what can fit in one subclass. I think this needs some of that culling. Try to distill your ideas down to 2-3 major ways to express "thunderyness" via mechanics, and build around those.

Some examples: 

You might want to have Thunder Fist just allow thunder damage and increased range. You could tie the range to PB at PB * 5 ft so it starts at 10 ft and caps at 30 ft. You don't really want a range beyond that because a monk punching from 90 feet away is honestly just going to be boring to play. All your movement stuff doesn't matter if you don't need to move.

I'd probably scrap Pressure Augment entirely due to its similarity to Open Hand and pick one effect you want to apply. The Booming Blade effect would be fine, maybe scale it with the MA die. Or something like a bonus action/FOB variation that deals MA+WIS thunder damage to all adjacent enemies.

Thanks for all the comments so far! Honestly, the idea to punch here and hit something somewhere else just popped in my head and I made this pretty quickly, not even thinking about the features of existing sub classes. I think all of your suggestions are very reasonable and I will rework my idea to a feature that requires activation like Barbarian rage, Astral Self, or Stars Druid.

Someone else I asked said that this class also has a major flaw in the 'Silence' spell. I don't think it's that big of a deal, but I'd like to hear what you think as well :)

Silence does render all the extra thunder type damage null, but it doesn't negate everything. In the original draft, Silence would interact like this:

1. Thunder Fist: the extra PB damage seems to also be added to unarmed strikes that deal bludgeoning damage, so if the player does not choose to deal thunder damage and uses bludgeoning instead, then Silence does nothing.
2. Pressure Augment: completely nullified, since it relies on the monk dealing thunder damage, and Silence prevents that.
3. Flying Fist: since it affects your unarmed strikes, regardless of the damage type, then Silence does nothing.
4. Dance of Thunder: first half is unaffected by Silence, the second half is completely nullified.
5. Warrior of Thunder: same logic as with Flying Fist and Thunder Fist, as long as the player doesn't choose the thunder type, Silence does nothing.

So the only features really affected by Silence are Pressure Augment and the second half of Dance of Thunder.