There seems to be quite a lot of confusion as to how we know what we know. First, fleet composition.
I personally saw, and reported to my superiors, the rough number of your vessels in Delta before the fight with the Keepers broke out.
Now, about the Gallia thing. We know this because we had a Maquis contact us. We asked him to gather intel and he confirmed a rough number of your ships and stated they were looking for SCRA Operatives. Now, because you sent an entire Armada instead of just a ship or two to gather information about the SCRA, we began to suspect an attack and began making preparations for it.