And then I hit a wall. Did make me think about a few more options, such as instead of hitting the generator hit whatever is powering it and we didn't think about how the Union could get past the shield in a scientific fashion... I can't think of anything yet...
Say how are the generators powered? Giant battery, hamster on a wheel, nuclear station?
I doubt that Cannes has somehow persuaded one or more of the factions on Alura to help him, if they are unified against all outsiders.
They cannot land outside the shields (like with the Battle of Hoth) because the shields are all-encompassing, but is it possible that they could bombard the shields until they give out from the strain of heavy orbital bombardment? It could take some time and their control ship might be knocked out in the mean time.
I doubt they could deploy something(s) so lethal that they could take out the shields by themselves. The BV-50 is a nasty machine but it couldn't do that... right?
How exactly do the turrets that fire at you after you come through the shield work? What are they set up on? Will they fire on targets only big enough to be recognizable? How small was the prototype droid that brought Xeth and the other renegades down? Was that a one of a kind so far prototype droid?
The Trade Federation Battleships are exceptionally heavily shielded and loaded out with any many gun batteries but the guns are of standard yield and would never breach a planetary shield.
The Colonel tells you, Vlad, that the sensor net will detect any reasonable space-based object- all the way down to fighter size.
And so then to answer your other questions- the BV-50 was smaller than a human, and it is absolutely one of a kind (though Cannes would have talked more about that if asked).
Suddenly you feel very unsure of yourself, Vera...
All the way down to fighter-size? And the BV-50 is smaller than a human... so the sensors that operate with the defenses would not detect it. Not to mention that it is mobile enough to avoid heavier guns.
They could deploy the BV-50 from space, have it slip through the shield carefully so that it would not damage itself, then go on to attack shield generators! And nobody could stop it because it is shielded, so conventional blasters would never get past its defenses and it would completely annihilate everything that stood in its path!