If you are used to something, it is familiar. You hear this as "I'm used to it," meaning "That doesn't bother me any more." You might also hear "He's used to winning," meaning that he has always done well and expects to continue doing it.
"Penniless" is not an idiom. It means that you don't have a penny to spend. It's used as an exaggeration to mean that you don't have any money.
Idiom
This is not used as much as it once was, but people will know what you mean if you use it; it's not obsolete.
This is unclear -- do you mean "what are some idioms used in the movie?" Because "inception" is not an idiom. It's an ordinary word.
An idiom usually is a sentence, or part of one. It certainly can be used as part of a sentence. The way to tell if it's an idiom is if it makes sense the way it's literally written.
The idiom you have alluded to means to be placed precariously or unfavourably in a situation. The American expression "skating on thin ice" has a meaning that is synonymous and can be used interchangeably with the idiom in question.
It's not an idiom. To break camp means to break it up, to pack your things and leave the area. It can be used as slang, however, to mean a group "packing up" and leaving.
It's not really an idiom. It means "what are you thinking about."
RFP is not an idiom. It's an abbreviation.
It is not an idiom, it means your nose is itching.
together mean something different than when they are used separately
Nothing. I think you may mean "mend fences," which literally means to repair or fix the broken spots in a fence. Used as an idiom, it would mean to fix or repair a "broken" relationship by apologizing, compromising, and communicating.