I believe that all of your questions can be answered by explaining the underlying threat when running any relay on the same Tor as a hidden service:
Relays publish bandwidth information about their usage and availability to enable the Tor network to efficiently route traffic and provide bandwidth where it is needed. Given that I see bandwidth information about your relay, I can potentially link your hidden service to your relay by tracking the popularity of your hidden service over time) and watching your relay's available bandwidth fluctuate.
I can track your popularity over time by setting up a relay and getting it the HSDir flag which allows it to become a location where service descriptors can be retrieved from for a hidden service.
By modifying my relay's Tor to log hidden service descriptor requests, I can extrapolate how popular your hidden service at a given time.
After I have managed to correlate your hidden service with your relay, if I decide to use your relay as my entry to Tor, I now have your IP address, allowing me to correlate your IP address with your hidden service.
Long story short: Don't run a relay on the same instance of Tor as you run your hidden service.
Example of tracking hidden services
In addition to being able to be tracked generally by a HSDir relay, you can be targeted more directly by a determined and powerful opponent because they can maintain the connection to your hidden service and they can pull a lot of bandwidth through the network separately to observe where things slow down when they are hitting your hidden service hard.