What CRM I should use?

Hi!

I'm looking for a CRM Solution for a software engineering company. Our case is the following.

We have a Salesforce team whose job is to bring clients (projects) for the business. Each Salesforce member could be associated with 0 client, 1 or many clients.

I'm looking for a CRM system which allows me to create different types of user roles. I want to have a user role called Manager which deals with all crud operations on the CRM system. On the other hand, I want to create another user role called Salesforce which is a view only user role.

Important points to mention

• The Manager user role is allowed to add clients with their respective
  contact details and assign each client to the sales force member who
  brought the client.
• The Manager will mention all payments paid by the client and what payments the client has in the future.
• Sure, the manager job is not limited to these. The manager is able to do any CRM related task provided by the system.
• A Salesforce is only allowed to view all clients that the manager has
  assigned to. The Salesforce member is not allowed to view clients which are associated with other Salesforce members.
• A Salesforce can view information about clients such as contact details, payment information etc..

I prefer the following.

• If the CRM could be hosted on my cloud hosting server.
• Ability to modify the CRM's code.

I'm not looking for an advanced solution.

What CRM solution do you recommend?

Thank you.