What should be considered before changing the field type of a custom field?

Sales reps at Get Cloudy Consulting want to see a visual representation of their emails and phone calls with a contact.
Which contact record component must be present so users can see this?

A Salesforce associate wants to learn more about an app to see if it would be a good fir for a business need, but they are not a system administrator.
Where can they learn more about the app?

Which tool creates a visual representation of objects and their relationships?

Get Cloudy Consulting (GCC) currently supports its customers via calls and emails. GCC wants to meet the needs of digitally savvy customers by offering support via web chat as well as SMS, Facebook Messenger, and whatsApp.
Which Salesforce product should meet this need?