Assign Existing Lead to Campaign

Assign Existing Lead to Campaign

ZOHO CRM seems to operate on the premise that leads are generated BY campaigns. I have a different approach. For me a lead is a "suspect" someone I think might be a possible client in future. I gather these leads in various ways, research, lateral thinking etc... I enter them in CRM as leads and later I want to run Campaigns in which I will target some or all of these leads by sending them marketing literature etc... by email or direct mail or perhaps just a phone call.
So I create a Campaign. What I then want to do is "associate" existing leads to this campaign in as automated a way as possible.

To complete the picture, having run the campaign, all leads with whom I have made contact become Accounts/ Account Type Prospects and with Contacts, Potential etc... As I make more contact and learn more, I will qualify these prospects until eventually, I hope, I will convert them to Account /Account Type Client.
I hope my approach makes sense, but  I would appreciate any guidance on how to achieve what I need.
Many thanks
Denis