Just a suggestion for the course. I find it very disruptive to have the words introduced as plural, before having seen them as singular. If the course could improve this, I would be happy. I know it's not the place for report here, but no way to report that kind of things, and maybe some other people will agree with me.
I don't say it's impossible to learn the plurals first, but it requires more effort, and it's a less natural (and efficient) way of learning.