When selecting your PHP version (5.3 or 5.4) in most cases the default extensions and settings should be fine. Unless you know what you're doing, adding or disabling extensions or settings can cause issues.
Most hosts set default PHP extensions and settings that will meet the requirements needed to run the more popular scripts provided by services like softaculous, such as Wordpress, Drupal, Etano, etc. Any special requirements will usually be listed in the Etano online documentation:http://www.datemill.com/etano/wiki/doku.php?id=requirements
Not all shared hosting is created equal and the most common issues for running Etano effectively are shared hosting that only provides PHP versions above 5.4, strict security restrictions or limitations on resources, don't allow crons to run every 5 minutes, etc. Most of which you will have little or no control over and will either need to try and get support from the host or find another host or hosting plan that provides the requirements needed.