Explanation
Before save flows only support four elements: Assignment, Decision, Get Records, and Loop.
References: https://help.salesforce.com/s/articleView?id=sf.flow_ref_elements.htm&type=5

Explanation
Formula fields are types of fields that calculate a value based on an expression or formula that references other fields or constants. Formula fields prevent administrators from changing their field type once they are created because they may be referenced by other functionalities such as reports, validation rules, workflow rules, etc., that depend on their data type and value. If a formula field is referenced by other functionalities, then changing its field type may cause errors or unexpected results. References:
https://help.salesforce.com/s/articleView?id=sf.fields_about_formulas.htm&type=5

Explanation
A PriceBook is a feature that allows administrators to define different prices for the same products based on different criteria such as customer segment, region, channel, etc. For example, a PriceBook can provide reseller partners with discounted prices on the products they purchase compared to regular customers. A PriceBook consists of one or more PriceBook entries that specify the product ID, pricebook ID, list price, currency, and active status for each product-pricebook combination. References:
https://help.salesforce.com/s/articleView?id=sf.pricebook_overview.htm&type=5

Explanation
Expected revenue is calculated as Amount x Probability. If the expected revenue field displays incorrect values, it means that the probability associated with the stage is not accurate. The administrator should change the probability to reflect the actual likelihood of closing the opportunity at that stage. References:
https://help.salesforce.com/s/articleView?id=sf.forecasts3_expected_revenue.htm&type=5

Explanation
Custom object and master detail field are two steps that should be configured to meet this requirement.
Custom object can be used to create a new object for shoe design that can store information about different designs and stages. Master detail field can be used to create a relationship between Product and Shoe Design that prevents deletion of Shoe Design records and allows multiple designs for one product. References:
https://help.salesforce.com/s/articleView?id=sf.customize_customobjects.htm&type=5
https://help.salesforce.com/s/articleView?id=sf.relationships_considerations.htm&type=5