Do I need both CRM and Campaigns? And best practices.

Do I need both CRM and Campaigns? And best practices.

Hi Everyone. I have done a bit of research and feel good Zoho. I'm especially interested in the possibility of campaigns and CRM integration but I have some questions.

QUESTIONS
  1. Do I need to work with both CRM and Campaigns? Are they redundant? Or do I need both for different tasks?
  2. I want to import my existing MailChimp email subscriber lists (with various custom fields) but I'm not sure if I do that into Zoho Contacts or Campaigns or CRM? What are best practices? 
  3. In further detail, I have various email subscribers in segments with custom fields but the fields in Campaigns seem to be quite basic and I didn't find areas for importing and mapping custom fields. How do you add custom fields and map them accordingly? This is very important.
  4. For any duplicate subscriber info, is there an easy merge function?
Thanks for your attention and answers in advance. 

:) Michael