Hi mshahnawaz1 
I believe that there should be no need to store the uploaded listening history file in the db after the listens are successfully imported
Regarding your second query, I think it would be better to use the already existing api endpoint (submit-listens one) as it is already tried and tested & also, we can submit listens upto 50 at a time so it's convenient

As far as mapping listens is concerned, listenbrainz already takes care of it
There is a complete automatic listens mapper which maps submitted listen to the MBIDs 
So we don't need to take care of it 😄

I might be wrong though
@luf