It's true that the United States does not depend on food and energy imports. However, the growing fiscal situation and unsustainable costs of maintaining global hegemony are very similar to that of Britain in the 20th century, as is the declining competitiveness of American industry. You're never going to find any exact or perfect historical parallels but there are enough similarities to cause concern.
No, it really, really isn't. The key difference is that the US can finance deficits and Britain couldn't. There's huge appetite all over the world to buy US government debt and to invest in the US. The UK needed massive foreign aid just to survive.
As long as you can still find someone to lend you money, debt isn’t a problem? Good to know.
The US is not really in trouble because of maintaining global hegemony. It’s in trouble because of repeated tax cuts by Republicans that are too popular for Democrats to fully unravel, and deficit spending largely caused or enacted by Republican administrations. Maintaining global hegemony really isn’t that costly to the US as a percent of GDP. It’s foolishness like the Middle East wars that are costly.