Debt is not a problem, it's how you pay it off. Every country has a credit score as well. The higher the credit score for a country, the more money it can borrow. And if the country borrows too much, it gets down rated. Just like it happened with France recently, when they got down rated from AA to AA-.
The US can borrow shit loads because it has a very high credit score and it pays its bills without a hitch.
Mmm, yes, you are allowed. You can't print existing government backed currency, but you can print your own. And plenty of companies and individuals are doing that.