Drupal data entry forms & db structure?

I'm trying to build a Drupal site in which users can input records containing data about "customers", "employees" and "sales".

I would like to be able to create a form(s) which takes data about a sale/customer/employee and can be associated with a record of a customer/employee(who made the 开发者_运维技巧sale)/sale.

I would also like to be able to display records showing a list of sales or customers or employees in which when clicking one record, it will open a page displaying all the relational data.

I'm new to development and am searching around like a headless chicken lol. I was thinking of using content types for sales/employees/customers and using individual nodes for each record then using something like views to displays filtered lists, but I am unsure if this is the best way to go about/structure it (maybe I should use separate custom tables or database and use a custom module to fetch the data?). It would also be nice if some of the fields can populate other fields based on it input and also if some fields can utilize a sort of auto-complete by garbing data from other records, or is that asking way too much?

Thank you for any suggestions you might be able to give me.

I, for one, would certainly prefer using a custom separate database and leave drupal databases to its own devices, if you would ever need to upgrade the site to a higher version of drupal it helps if you don't modify it, and also consider using webform (http://drupal.org/project/webform) as it makes development easier both in components and hooks.