The SDN consensus seems to be that informal vs formal is a matter of personal preference-no one cares whether you get a little certificate at the end or just register independently.
However, I have seen people on here say that it looks bad to take postbacc courses at multiple institutions without good reason. Is this true? No idea, but I've seen it in threads here.
Especially coming from Penn-some people on here might say it'll look like you're avoiding more difficult upper level courses there. But-your postbacc GPA is high, Penn is expensive, and your family is far away.