A hundred robots, solid robots with EMP shielding, sufficent AI to fight and a power-pack that lasts more than half an hour, would cost an insane amount of high-tensile alloy, so they don't get blown apart by the first bullet. And you need millions. Plus, piracy and fleet's ambushing convoys takes about 20-40% of the income from other worlds, import prices will go though the roof because your at war and the exporter will bleed you for that very reason, and then you need to create air units, mechanical divisions, Space-ships, and the weaponry. The demand would be astronomical, and so even if you won, you'd have to strip-mine half your empire just to have forces to meet the enemy. 

So yea, the greatest enemy would be your own army.