Don't forget you can multi select (shift or ctrl click) songs and edit them all at once. Start of with Genre to get it narrowed down.
Someone could probably give you suggestions on finding an app that uses the Music Brainz service. The one I use is Mac only. It will preview songs and give you sugestions on what it is. You select the right one and the important tags are done for you. Once you have all the album names filled in, sign up for a iTunes account and you can go to the advanced menu > get album artwork and it will download the correct album art.
Also, double check where your old directories of music were. Chances are, your iTunes Library is in a different location and iTunes has doubled up the space it's taking up. Delete the old location when you are VERY SURE that it imported everything.
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