Question: What I need is to clearly differentiate between the attachments (this is an approval, this is an offer, this is a PO, etc).
Is this possible, or it is working only in bulk (attach all files together)?

Thanks,

Answer: 
SharePoint does not support attachment metadata. I would suggest storing the attachments in a document library (probably with Content Types for Approval, Offer, PO, etc) with a lookup column to the associated item in your list.
There are two option.

1. Add as many attachment you want to attachment column with the list. but you cannot associate metadata with that.
2. Create document library and use lookup in the list to view name of the document. so in a way it is storing the common document in library and just refer which one you are supposed to use.

Custom code is another one.