To answer your questions:
2a. Yes, it is a shorter version and yes both are correct.
2b. No, it is not literally talking about distance.
2c. "One blow from caving in" means that if the house of cards receives one more blow, then it will cave in (collapse). We can use "from" or "away from" to say that if one more thing happens, then some other thing will happen.
a. I need to pass seven exams to get my university degree. I have passed six exams. >> I am one exam (away) from receiving my university degree.
b. I have $90. I want to buy a new mobile phone for $100. >> I am $10 (away) from having enough money for a new phone.
NOTE: the form is: away from or from + gerund (not infinitive).
I hope this has helped you!