A final piece of advice before we launch into building your Drupal site: buy a notebook and keep it next to your computer. Use this notebook in the same way a ship's captain uses his/her log by taking brief notes on what you do and why.
In the process of building your site, you will make decisions about module configurations, user roles, design tweaks, and so on. As you are making these decisions, you will be fully convinced that you will remember each decision you made and why.
Unless you are the exception that proves the rule, however, you won't remember. And this is where your notebook comes in. Use the notebook to record the changes you make. A useful entry will include the URL where you made the change and a brief description of why you made the change.
For example, if I am adjusting user privileges for the authenticated user role, I would enter the following in my notes: At admin/people/permissions/2—adjust user privileges so that the authenticated user role needs to have comments approved.
This way, when you are trying to remember why you made a specific change, you will have a record of your decision-making process.