Tor relay security

[onion.soup at nym.hush.com]

I come across How to Run a Secure Tor Server at: 
https://wiki.torproject.org/noreply/TheOnionRouter/OperationalSecuri
ty and have some questions I could not get answers on my own, 
limited by my knowledge.

1. The article talks about encrypting sensitive information on a 
Tor server. Does the author mean that files on hard disk are 
obtainable by other Tor users when I run a Tor relay? How likely is 
that going to happen? What platforms are more vulnerable in this 
aspect?

2. I noticed there are key files found on machines running as Tor 
relays. But I get no idea how do they come into place. Are they 
generated automatically when I configure my Tor as a relay? as a 
client? And do I get a new key each time or does it ever expire? 
The article talks about safeguarding the key. I read that Tor 
employs asymmetric key so I suppose that key is my private key. If 
that key is compromised, does this (a)reduce the entry node's 
certainty about whether the packets are originated from me and 
(b)allow anyone with that key to decrypt packets destined to me 
from entry node?

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