To get the first look what Graylog is and how you can work with we have a virtual appliance to run on VMWare or Virtualbox. The following will guide you to start using Graylog.
After you feel comfortable you should make a fresh installation that takes care of your recommendation regarding the sizing and the security settings. The virtual appliance is only created to have a showcase about the features and is not created to run in production.
If you need assistance to plan and build your logging environment we offer professional support that can work with you.