Beat in mind that if you're choosing a lot from the same album, it might be an idea to just buy the album for the extra $2/3 I've done that occasionally over here.
The other thing is that you know you can create a playlist in iTunes with all those songs dragged in from the iTMS. Then when you're ready to buy, you can click Buy there rather than having to navigate to each one afresh. And when you've bought them, they change in the playlist so it's easy to clear out the ones that are still there.