From testing I did several months ago here are some observations I made about how models work in BC and some of their limitations.
1: It appears that each element of a model (each section of it) has a limit of approximately 97,821 triangles
2: Elements of a model can be combined (like the nacelles on the stock galaxy class are their own element) to have a total of around approximately 166,658 triangles
3: The game appears to have an extremely high limit on the total amount of triangles it can display, a ship that has the max 166,658 triangles can have many multiples of it loaded on screen without issue (for my test I had a total of 10,666,112 triangles on screen)
4: The game has a hard time when vertices too near one another, on high detail models this will cause faces to not appear in game.
Here is 27 stock galaxy models compressed into one model element, 97,821 triangles
Here is 81 stock galaxy models compressed into one model element, 293,463 triangles. Notice how the nacelles have vanished off of 2/3rds of the ships, they are being culled due to limitations.
Here is many hundreds of stock galaxy models that were combined into groups of around 30 (I don't remember). Total onscreen triangle count is 10,666,112.
Example of a high triangle count model that has vertices too near one another.