I am attempting to learn how to modify invoice templates in Odoo v8. I have searched these forums and read a lot of different information but I am unclear as to the proper procedure in Odoo v8. 

I'll start off with what I have already tried:

1. Using the HTML WYSIWIG editor to modify invoices
   I found information in other posts about modifying invoices this way.
   Here are the steps I followed:
       #1 Go to Settings > Reports > Reports > Invoices and change the Report Type from PDF to HTML
       #2 Go to Accounting > Customer Invoices > Open an Invoice > Print > "Invoices" 
       #3 A  new pop-up window appears. This window does have the HTML WYSIWIG editor enabled. 
       #4 If I make modifications here and change things, then AFTER hitting SAVE it does NOT make these changes permanent.           I.e. I I open another invoice and select Print > Invoices again then I see the original default template. 
   
   QUESTION #1: How do you make changes you make using the WYSIWIG editor actually save permanently to the invoice template?
   EDIT: I was wrong. This is actually working just fine. I was trying to modify the HEADER/FOOTER areas which you can NOT edit via the HTML Editor while viewing an invoice. 
    
2. Edit QWeb Views
   I also found some information in the forums about modifying invoices in this way. 
   Here are the steps I followed:
      #1 Go to Settings > Reports > Reports Invoices
      #2 Select "Search Associated QWeb Views"
      #3 Click on "report_invoice_document"
      #4 Modify the HTML layout
      #5 After modifying this layout I was successful in seeing my changes outputted to the invoice template. However, through modifying the invoice template in this way I was NOT able to edit the invoice header. I assume I must modify this elsewhere and will add details about that in the next item. 
   
   QUESTION #2: Where do I modify the header that effects Invoices? 
   EDIT: I have answered this in my reply/answer below. 
   
    
3. Modifying the Invoice Header
   Since I was unable to modify the invoice header in the QWeb Views "report_invoice_document" I searched for where to modify it. 
   These are the steps I followed:
      #1 Settings > Companies > Companies > "Company Name" > Report Configuration (tab) 
      #2 I modified the HTML for RML header. 
      #3 When I previewed it within the "Report Configuration Tab" it looked CORRECT. 
      #4 HOWEVER, these header modifications did NOT take effect in the actual invoice. 
   
   QUESTION #3: Which of these two methods (QWeb View vs. WYSIWIG) is the proper way to edit invoices in Odoo? Or, is there another, better way to do it?
   EDIT: It is correct to use either the QWeb View -or- the WYSIWIG mode. They both effect each other. I found the QWebView/HTML Editing to be the only option to get the results I wanted. 
    
4. Multiple Invoice Templates
   I would like to have two different invoice templates that appear when selecting "Print" from the drop down menu.  I am not sure the correct way to do this. I did try duplicating the "Invoices" item under Settings > Reports. The new item did not appear under the "Print" menu so I assume I am not doing this correctly. 
   
   QUESTION #4: What are the proper steps to create multiple invoice templates that can be utlized via the "Print" menu?