I've set up a workflow so that a new client email gets sent out to our onboarding team every time an opportunity is closed-won (new client email includes details of the deal).  I have it set up as follows:

Evaluate the rule when a record is:  created, and any time it’s edited to subsequently meet criteria
Run this rule if the following criteria are met (Opportunity: Stage equals Closed Won).

After an opportunity is closed-won, if the reps decides to go back into the opportunity to update a field, it sends out another new client email.  Which field do I need to change so that it does not send multiple new client emails?

Is it possible to give someone transfer rights to a specific group of user's accounts/contacts/leads without using the role hierarchy?  

I can't figure out why this validation rule isn't working.  I want to make it so that if C4A or C4A Single-Channel is selected from my "Product" pick list, then the opportunity cannot move past the "Qualified" stage when "N/A" is selected from the "Product Engineer" picklist.  I also only want this to apply only to the record type "Sales".  But for some reason, when I apply this validation rule, I get the error message even when I'm in the Qualified stage.  

Here are the picklists I have, including what fields are available for each pick list:

Product:  C4A, C4A Single-Channel, C4N
Product Engineer:  N/A, (then multiple product engineers)
Opportunity Stages:  Qualified, Scoping/Presentation, Negotiation/Proposal, In Contract, Closed Won, Closed Lost
Record Type: Sales

Here is my validation rule:

And (
ISPICKVAL(Product_Engineer__c, "N/A"),
($RecordType.Name = "Sales"),
OR (
ISPICKVAL(Product__c, "C4A"),
ISPICKVAL(Product__c, "C4A Single-Channel"),
OR ( 
ISPICKVAL(StageName, "Scoping/Presentation"),
ISPICKVAL(StageName, "In Contract"),
ISPICKVAL(StageName, "Negotiation/Proposal"))))

Is it possible to give someone transfer rights to a specific group of user's accounts/contacts/leads without using the role hierarchy?  

I can't figure out why this validation rule isn't working.  I want to make it so that if C4A or C4A Single-Channel is selected from my "Product" pick list, then the opportunity cannot move past the "Qualified" stage when "N/A" is selected from the "Product Engineer" picklist.  I also only want this to apply only to the record type "Sales".  But for some reason, when I apply this validation rule, I get the error message even when I'm in the Qualified stage.  

Here are the picklists I have, including what fields are available for each pick list:

Product:  C4A, C4A Single-Channel, C4N
Product Engineer:  N/A, (then multiple product engineers)
Opportunity Stages:  Qualified, Scoping/Presentation, Negotiation/Proposal, In Contract, Closed Won, Closed Lost
Record Type: Sales

Here is my validation rule:

And (
ISPICKVAL(Product_Engineer__c, "N/A"),
($RecordType.Name = "Sales"),
OR (
ISPICKVAL(Product__c, "C4A"),
ISPICKVAL(Product__c, "C4A Single-Channel"),
OR ( 
ISPICKVAL(StageName, "Scoping/Presentation"),
ISPICKVAL(StageName, "In Contract"),
ISPICKVAL(StageName, "Negotiation/Proposal"))))