Explanation
To create a contact and an opportunity from a lead that is associated with a campaign, and keep the campaign member history, the administrator should convert the lead from the campaign member detail page. This will automatically create a contact, an account, and an opportunity that are linked to the campaign. Deleting, cloning, or adding a contact will not preserve the campaign member history. References:
https://help.salesforce.com/s/articleView?id=sf.campaigns_leads.htm&type=5

Explanation
Big Deal Alerts are notifications that are sent to users when an opportunity reaches a certain amount, probability, or stage. They can be configured by administrators to alert sales reps or managers when they have a high likelihood of winning a big deal. Key Deals are a feature of Einstein Opportunity Scoring that shows the top opportunities based on their score and stage, but they do not send notifications. Activity Timeline is a component of Lightning Experience that shows the past and upcoming activities related to a record, but it does not notify users of big deals. Performance chart is a type of report chart that shows how well users or teams are performing against their goals, but it does not alert users of big deals. References:
https://help.salesforce.com/s/articleView?id=sf.forecasts3_big_deal.htm&type=5

Explanation
Lead assignment rule is a feature that can be used to route new leads to the correct sales person based on the lead address. Lead assignment rule can assign leads to users or queues based on certain criteria, such as lead source, industry, or location. Lead assignment rule can also send email notifications to the new lead owners or other recipients. References:
https://help.salesforce.com/s/articleView?id=sf.leads_assignment_rules.htm&type=5