the fred ship count is the limit, i actually did a boe mission before however even as i hit the limit with at least 40 cap ships and many many fighters, it did many weird errors i removed one ship and it was all fine.
(i have found the inspiration i need for the 3rd mission in my b5 demo campaign).
i dont see much point in a background battle, unless its a feel of being in a big fight against your enemy.
besides this "into the fire" mission, the shadow fleet in the b5 mod doesn't have that cloud with the superstructure inside more or less rendering this mission fiction and not canon, so pretty much irrelevant imo.