Some of the other measures that I've taken:
Another full load of STO turrets is on its way to Harmony, again being dragged there by a super-tug to save time. Also a Tank Brigade is en route.
Several sets of Sabres are en-route, for jump point defense.
Enough Gadgets (small orbital workshops) and Devices (large orbital workshops) have been assembled at Harmony to support Force Randakar.
More colonists have been unloaded at Harmony, bringing the population up to 400,000 (and up to 600,000 once the en-route pops arrive).
Refueling and re-arming stations have arrived and unloaded. Tankers have arrived to transfer fuel, and ammunition ships are en-route.
Naturally, the more stuff we commit to the Harmony system the better our chances of intimidating or defeating them, but the more painful a defeat would be.