1. There are a lot of free flight servers on-line 24/7. You usually can enter them without a password. Just try. You won't mess up anyone's race because there is usually no race when the server is without a password. Just free flight.
2. The best way to join a competition is to find the competition's website first and then register to the website and/or competition. There you will get info about the race. Times, Rules, Servernames, Passwords, etc... usually you will get more info about the task (and password) an hour or 45 minutes in advance by e-mail or by login in to the website. I don't fly the US Nightly... http://gliderracing.com/pub/http://www.condor-club.eu/comp/competitions/202/http://www.virtualsoaring.eu/?lang=en
3. Yes. Your CN is the CN in Condor. For a competition they will have to be the same otherwise you won't get scored. The server has nothing to do with your CN. If they are not online then you won't see them.