Ok. Here is what I would do...

I would Pick my battles. Decide what is winnable and what is really important.

I would focus in on the lack of accommodation. This is federally mandated. The head TA moving up the exam like that is a very big deal. It might potentially have affected your performance and grade. Also, it is not in the syllabus that this can happen. Basically head ta violated the syllabus. This is also a very big deal.

I would schedule a face to face appointment with your learning disability coordinator. Email is not working. For this meeting, I would print out every email, all sides (mine included) relating to this issue. Arrange them chronologically. This is your proof. Printing and arranging is time well spent.

At this time, I would suggest that the head ta is not understanding accommodation. Request a meeting (soon) between coordinator, head ta, and yourself for clarification purposes. For that meeting take all printed emails too. Again, proof is incredibly important.
(The head ta will hate me, but this has to be dealt with ASAP.)

Then, I would do some serous thinking about prof and all TAs disorganization. I would ask around about other large intro classes at your Uni. Is this completely out of line?

I highly suspect it is not. Profs don't care at all about intro classes. Some don't care about any undergrad classes. It's the nature of the beast of higher Ed.

I would not complain about disorganization of prof or tas to learning disability coordinator. Even if the LDC is sympathetic, it is completely out of anything they can help me with.

I would try to be proactive. The tas are lousy in the discussion group. TAs are pretty much always a walking disaster. Ok, undoubtedly other students in the group are frustrated and worried about grades. However there is a built in peer study group right there. before discussion group ask who wants to go after to a close coffeehouse and review. Or set a convenient time weekly to meet on campus and work on stats problems together. Peer support, plus maybe make some friends.

This is solely what I would do. I know you are really frustrated and scared for your education. However most of what you described (non accommodations) disorganization etc. is really fairly common. It's annoying, but the nature of higher Ed.