Hi Jason,
I see some mistakes in your code:
1) Try to use double quote character " instead of single one ' in expressions like Documents["/Products"]
2) The expression Documents['/Products/All/' && SKUNumber] looks wrong because Documents object can load a document by index or NodeAliasPath value and it's not clear what you tried to do with AND operator. So here, I think you should use + operator, so expression will be like Documents["/Products/All/" + SKUNumber].
3) Property DocumentContent returns content of widgets or editable webparts, for example if you have editable text webpart with name EditableText1, you can get this value via DocumentContent["EditableText1"]
4) If you want to get some values from page type propertiesm, you can use the name of the property to get the value (example: Documents["/Home"].DocumentName) or use GetValue method (example: GetValue("DocumentName")
So your result expression will be like {% Documents["/Products/All/"+SKUNumber].GetValue("ModelName") |(identity)GlobalAdministrator%}. And Kentico has Macro Console in System Application, where you can check any macro expression and see how they work