Addition of custom-fields
Thank you for your interest in CiviCRM. Broadly, the answer to your question is 'YES'. 

Since CiviCRM is open source software it is possible to customise anything and everything. However, some things are much easier to customise than others. 

For example you can easily make changes to the configuration to do the following:


customise the user interface - including dropdowns, display preferences and search preferences
create custom fields
create profiles - to collect or display related fields


Other changes may require custom coding and so may require a developer to make the change for you (or you could learn how to do this yourself if you are that way inclined).

If you have specific questions about any of these topics it would be best to post them as separate questions. As mickadoo says StackExchange works best if you just ask one question per 'question'.