I'm thinking about multicasting a Monk with Astral Self with either a Ranger or a Fighter.  Was thinking about which fighting style would work best.  The Arms of the Astral Self are described as Monk weapons.  Can I take the Two Weapon Fighting style in order to apply my proficiency to Arms of the Astral Self? 

"count as monk weapons" != "count as weapons for all features"

They are not weapons. The phrasing of them counting as monk weapons means they can use your monk's Martial Arts die for damage. They are also considered unarmed strikes when you use them.

Your unarmed strikes already benefit from proficiency. This includes the 1 free bonus action hit and the 2 from flurry of blows if you prefer to use them instead.

Two-Weapon Fighting doesn't apply and even if it did would be completely irrelevant and useless.

Thanks.  I wasn't completely sure how that would work and didn't want to risk wasting the fighting style.

I would personally recommend Ranger since they love Dex and Wis as much as Monks do. That would also give you an extra level to make up your mind before having to choose. The reason that’s useful is because the new book comes out in 12 days and there will be more fighting styles in it.