Reading through everyone's posts about Astral self, everyone always seems to jump to level 17 and talk about the astral barrage and how much damage you can do. I'm trying to look at this subclass on the lower end of the scale. Level 3. Can someone clarify how many attacks you get and why it is a good class to have at the low levels.

From what I can grasp, you get one attack as an action and a second attack with a bonus action, so you're basically spending 2/3 of your ki points for necrotic or radiant damage and the added reach of 10ft instead of 5ft because monks already have a second attack as a bonus action. Is there something I'm missing here or is that about it? 

Thanks, Luke 

Consider a level 3 Bugbear Astral Self Monk. In dim light, their proficiency in stealth is already strong in evading perception checks. Add their added movement from Unarmored Movement and Surprise Attack, and they can run circles around anything without Darkvision with your 30ft sphere of reach. In darkness, they would be neigh impossible improbable to detect without decent perception. Additionally, at level 4 or as a multiclass, you can do a toned down Polearm Master cheese with Sentinel where you essentially have a 30ft diameter sphere that a single enemy cannot walk out of. This makes you a giant roadblock for your back line against 1-2 enemies (boss fights) if you couple it with stunning strike effectively. To me that just makes Astral Self an even slower build up Monk for greater reward in the end.

If my analysis is correct, that's just how I would break the class. There may be more.

I'm not 100% sure if this RAW or RAI, but between the Wisdom on Strength Checks and the description of the Astral Arms I'm assuming you can actually use them to effectively grapple a target while keeping them at 10 ft reach. Otherwise it's a rather strange thing to add in for the Arms themselves. 

This essentially makes the Monk able to pseudo-step into a 'defender' or 'tank' role in the party without losing what makes them a monk to begin with. I think the idea of this being a Grapple Monk also explains the later abilities like hitting extra hard on your first attack or the number of attacks when you get to the full Astral Self, they are expecting you to use some of your attacks to grapple a target, and those abilities soften the cost for having given up one of your attack rolls to grapple the target.

So from that perspective, the level 3 ability to keep an opponent creature out of range while pummeling them with your astral arms, at a level where you can easily be killed by 1 or 2 strong hits from a melee type foe seems worth the 2/3 points.

 Arms of the Astral Self key off Wisdom instead of Dexterity, which means you can invert your stat priorities if you want to focus on Stand battles Astral Arm combat.  Yeah, it takes most of your ki at low levels, but you can regain your ki with a short rest.  At 4th level you have two Astral Arm summonings banked up, and at medium levels - the 7-13 range, let's say - you can mix in Stunning Strikes with your Astral Arm blows and those strikes will have a higher than normal DC because an Astral Self monk pumps Wis instead of Dex.

Low-level Astral Selves needing to be choosy about when to use their ki isn't really unique to the Astral Self.  All monks have to be picky about when to burn their ki at the really early stages of the game.  What you get with Astral Self is a three-level head start on being able to pierce magical resistances, the ability to (partially) de-emphasize Dexterity if you'd rather play a Wise Old Stand Master Sage-type character, and tricks like a ten-foot grapple as Guytza noted.  Not to mention yeah, it's two ki points to conjure the arms...which stick around and do their thing for ten minutes.  One ki point, on the other hand, can be spent to give you one entire extra attack via Flurry of Blows at low levels, or to allow you to move more freely or dodge as a bonus once.  

The arms sticking around and doing their arm thing for an entire fight, or multiple fights in succession if they happen quickly enough, seems like a pretty decent deal to me.

Thanks everyone for the advice. It's really opened the class up for me and you've all pointed out some pretty good uses that I hadn't really considered. 

Thanks.

It'd only be a 20ft diameter sphere roadblock.  Bugbears only get the extra reach on their turn so you'd only get a 10ft from Astral Arms on other creature's turns.  You could forgo the Sentinel feat though and use stunning strikes instead since the Astral Arms do count as unarmed strikes now but that could eat up your ki points.  

If anyone has the old astral monk dm me plz, kinda wanna try it out

It’s kind of just worse than the final version, but here is is:

https://media.wizards.com/2019/dnd/downloads/UA-WildAstral.pdf

Thx!

How many arms do we get? Like, if I have a warforge monk and summon the arms, is it just another two astral arms, and he can make four total unarmed strikes? It's unclear exactly how many arms I can summon but I assume it's just like another two. Do I make those attacks on top of the two unarmed strikes I can take each turn as action + bonus action? It's not very well-explained! 

I'd say that if you want the image of summoning more than two arms then you can describe it that way for flavor but you are still limited on how many actual unarmed strikes you can make based on the subclass mechanics.  The Astral Arms can be used to make unarmed strike in place of your normal arms so you make 1 unarmed/Astral arm attack, 1 Extra attack after level 5, 1 unarmed/Astral arm bonus action strike or 2 unarmed/astral arm bonus action strike with Fury of Blows, and 1 additional Extra attack at level 17 if you use the Astral Arms for all three (non-bonus action) attacks.  At level 11 you can also roll an additional martial arts die on damage for one of your Astral Arms strike once per turn.  So at level 17 its almost like you get 6 Astral Arm attacks every turn as long as you have the ki points to spare, so like I said earlier I could see describing your character as have more than two astral arms for flavoring

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Also bugbear reach is only on your turn so that doesn’t really hold up.  But if you get them stun blocked on the first you I’m fairly certain you get 2d6 extra damage to each hit until they’ve been able to act on their turn but being stunned prevents their turn