I use the torque specs that come with the handlebar. You don't want to crush the bar, so look on the bar or on the manufacturer website for the specs.

I think turning the stem around would be a bad idea. For one, there could be clearance issues with the bar hitting the top tube. Your knees would likely hit the drops. Even if those clearance issues were solvable, I think it woul negatively impact the handling of the bike.