If you get your 10GH/s now, they will be paid for in 6 months or less, even if the difficulty reaches 100M in 6 months.
Unlikely. BTC/month will go about like this:
10, 7, 5, 3.5, 2.5, 1.75 = 29.75 btc in 6 months. The chance of making back 50 btc, ever, is relatively small.
Please show your math or these are just wild guesses. You must be taking BFL into account shipping all 60,000ish of their orders in the next few weeks or months to come up with those numbers.