So I really have no idea what I'm doing as this is my first pixiv upload. Please let me know how badly I fucked up the artist tagging, source posting, etc.
If the find artist function didn't work, before you create a new artist tag, you should search danbooru for posts with a source URL containing the artist's pixiv username. This lets you find if any posts by the same artist have already been uploaded. For example, the source URL of this post is http://img03.pixiv.net/img/a-s-a/1970361.jpg, so you should do a search for source:*a-s-a*. This time, I turned up three other posts by the same artist which have already been tagged with the artist name as, so you don't need to create a new artist tag. However, the artist entry does need to be edited to add a direct link to one of his images. In this case, I added the URL http://img03.pixiv.net/img/a-s-a/1970361.jpg to the artist entry. This is so the find artist function will work in the future.
If you do a search and the artist isn't already on danbooru, you'll have to create a new artist tag. See http://danbooru.donmai.us/artist/show/16197 for what a proper artist entry looks like. The most important thing is to include a direct link to one of the artist's images, as described above, so that find artist works.