I would absolutely get another 10 amps, run 500mg a week, split those into two shots a week.
Expectations depends somewhat on how you eat, but 20-25 pounds would not be abnormal on such a cycle.
Safe to buy online? Thats like asking how safe is it to rob a liquor store, you may get away with it and you may not, its illegal period. I know of a dealer that went down due to a mere case of odds being against him, eventually one of his packages bust open and they discovered it was not HotWheels he was selling but gear, so he got busted.
I would get an amp breaker, I hate amps. I actually use a dremel on mine with a cutting wheel, works great, but still a pain.