Yes, the one with the subject is more emphatic - intended to stress what is MY particular case, or WHO has a pen:is there a difference between "Yo tengo una pluma." and "Tengo una pluma."?
Yes, that's correct.So, the "yo" emphasizes the fact that I have a pen, as opposed to Dick, who has a pencil. Right?
"As for me" is quite an emphatic phrase."Yo tengo una pluma" meant "As for me, I have a pen."
I believe that "we" here means "we Spaniards." In Mexico, pluma is the most common word for pen, unless there is a need to specify that it is a ballpoint pen.(*) Bolígrafo / Pluma:
Note that we usually say 'bolígrafo'. Or 'boli', in its shortened, colloquial form. The term that kids use at school.