Drupal 7 - Advice needed to accomplish the idea of embedding a view in a view
Where did you read that Views is resource heavy?  While there is some overhead to running Views, it is generally not significant unless you are getting enormous amounts of traffic.  Your system sounds like it will be used internally, so I highly doubt that you will run into performance issues.

Views is a visual SQL query builder.  It is also the most popular module for Drupal and one of the best supported modules.  The alternative to Views is to write the SQL queries yourself, but unless you're a SQL expert this is error-prone and time consuming.  You can always do everything in Views first and then re-write some of the queries manually if you run into performance problems.