What kind of information does the broker sees?

Obviously they see entry points, SL and TP levels, but do they have access to some specific parts of the EA like comment, ea, name, etc.?

If it is not a marketmaker broker, then he only sees the essential information he needs to open an order. So the market price, when the order is / should be opened, the magic number of the EA and if you already set the SL and TP when the order is opened (you could also deliver them later if you want to). He is not interested in anything else.

Your broker would be handling enough data as it is by handling pending orders and market orders for all their clients across all financial products.
They would bother handling any other data.

Client side and broker side applications of Metatrader are designed to communicate only with information like connection details, orders etc. You can see logs of communication in the journal.