Hi Kristin
The short answer is yes to all of your questions. You can even have multiple vendors for one PO, record the invoice for the supplier and add the misc charges to the other vendors at a later time.
There is a setting in Company Profile that lets you decide how you want to allocate pro-rated miscellaneous charges in the case when the item has already been shipped - your options are to spread it over the unsold items, or to send it to a GL expense account.
Steve Schwartz