How to combine CRM and lead management?

Question

CRM

Dear users. Many questions have already been asked about crm. But, the question arose of a different plan
How to combine CRM and a lead management system (for working with clients and attracting potential clients)
A company in the b2b market.
A lot of crm has been considered. Liked amocrm, client base, zoho crm
Requirements:
1. A simple system system for managers
2. Correspondence with clients, comments, emails
3. Differentiation of rights
4. Work for 3-4 employees
5. Ability to automatically transfer data from forms (API is suitable)
Desirable :
1. integration with mailing services
2. possibility of integration with 1C and IP telephony (in the future)
Amocrm was a near perfect fit, but it's a lead management system and it's not convenient to manage existing customers.