I wanted to populate the data from Parent record to Child record on record creation or on  parent record edit , if the child record status is not closed . 

e.g : Parent record has customField1 and Child record has customField1,
I wanted to copy the parent record -> customField1 to child record custom field1 if the child record status is not closed .

Will the formula fields will be better option ? OR Need to populsated via triggerHandler ?

Could you please suggest 

I have a below requirement. Please suggest the best option to implement it .

Allow the user to create opportunity related record if the user has edit access on the opportunity. If user doesn't have edit access on opprtunity and tries to create the related record (e.g : Custom Object record ) throw the user friendly error message . 

We have multiple action buttons (images) on a page based on formula fields  . Click on any action button should check whether the current user has edit access to the record . If current user has read only access, display error message, otherwise proceed with existing action button functioanlity . There are several action buttons in a page and same logic should be applied for all . What is the best way to implement this ?
 

We have multiple action buttons (images) on a page based on formula fields  . Click on any action button should check whether the current user has edit access to the record . If current user has read only access, display error message, otherwise proceed with existing action button functioanlity . There are several action buttons in a page and same logic should be applied for all . What is the best way to implement this ?