One of the biggest problems I have found with midi or chord/lyric files is that the chords are not always correct.Some times the midi files are so simplified that it's hard to recognize the song. Because someone post the chords to a song does not mean they have the correct chord or position of that chord for the song. There can be a lot of cleanup to do. If it's for practice it will actually help to have to slug through some of those files.
To answer your last question, you can do almost anything you want, it just takes time. Wyndham