Hey @thefonebug, I'm assuming you have all the files sorted and named correctly, but no existing (or bad) tags, or similar? Now you are looking to just populate the tags?
Picard works best if you simply re-match/re-tag everything using its functions like 'scan' and 'lookup', as it's been created to work with the MusicBrainz database, not really as a tool for the kind of workarounds you're trying to do. If you use your music a lot, are interested in precise and flexible tags and data, or just have the time, I'd recommend using Picards inbuilt functions to simply retag everything.
If you want a hand with that, let us know!
The only reason I would see not to do is if you have a huge amount of music and just don't care that much/want the quickest fix.
I think @mfmeulenbelt meant for you to retag/match everything using Picard, and then overwrite the file names using that string - once things are matched with Picard you can very easily rename all of your music with one click (pretty much!)
Anyway, let us know what exactly you're after and why you're choosing this method. Maybe someone can help you with tagging from filenames as well, or recommend a different tagger.
ps. Just to reiterate, back up your files first. If you're trying out different programs and settings this is really important!! We can offer you a shoulder to cry on later if you don't, but our shoulders are starting to get salty and crusty