Help with bitocin.conf - how to configure a testnet full node in a safe way?
You should use the one provided in the Bitcoin Core repository which you have linked above. That one has everything disabled by default (so only defaults are used and it will run fine out of the box and use the mainnet). All of the options that you are going to ever use are listed in that conf file with instructions on what they do and how to use them. They're all commented out.


  Maybe, I have to put it in another format, since it is meant to be a conf file for the bitcore implementation


You will need to do that because that format of conf file (JSON format) is not supported by Bitcoin Core.

The questions you asked regarding the bitcore conf are completely irrelevant to Bitcoin Core as it does not support those options.



Alternatively you can use this Bitcoin Core configuration file generator which lets you choose the options you want to enable and it will generate the file for you.