custom content types

I have been hired by a client to build an intranet RDBMS for them to keep better track of their client information and appointments. I want to use Drupal 7 as opposed to a custom PHP/MySQL setup, as it has so many pre-buit functions that cut down development time. I am torn between the best way of going about this. I know to use Views in any case, but should I create custom content types, use Webforms, or a combination of both? I ask this because in pure database terms, the data tables will need to have a relational reference to one another (i.e. foreign keys).