The Assignment Rule checkbox is a checkbox that appears on manual case creation pages when assignment rules are defined for cases. The Assignment Rule checkbox determines whether or not to apply assignment rules to manually created cases. If the Assignment Rule checkbox is selected by default, then any manually created cases will be assigned according to assignment rules instead of being owned by the agent creating them. To prevent this from happening, an administrator can either deselect the Assignment Rule checkbox when creating cases manually; or change the default setting for this checkbox under setup by selecting or deselecting Use active assignment rules by default. Reference: https://help.salesforce.com/s/articleView?id=sf.customize_casesupport_assign.htm&type=5

Assignment rules are tools that allow administrators to automatically route records to users or queues based on certain criteria. For example, an assignment rule can assign cases to different queues based on case priority, origin, type, or other fields. Assignment rules can be triggered when records are created manually, via email, web, or API. Assignment rules consist of multiple rule entries that define the criteria and actions for each assignment scenario. Reference: https://help.salesforce.com/s/articleView?id=sf.customize_leadrules.htm&type=5 https://help.salesforce.com/s/articleView?id=sf.customize_casesupport_assign.htm&type=5

To make sure the custom picklist field values are populated on contact when leads are converted, you need to create a custom picklist field on contact and map it to the corresponding field on lead.

Record types allow you to update the options in a picklist based on the kind of opportunity.

Record types and sales processes allow you to have different page layouts, fields, required fields, and picklist values for different types of opportunities.