I think that one of the discogs scripts allows to search by title and artist.
As for the other things just something to think about:
The combination of artist and title is not really unique as the same title could appear on the single, the maxi, an album, the greatest hits, the golden hits, the live album, a top twenty collection and so on. You would have to identify which is the likely version.
If you have artist and title in the filename, then use the Convert>filename-tag function to import the data first into the tags and then use a tag source - with all the limitations I already described.