Sounds like some great ideas to me!

I like the idea of having the assignments posted on each level, so students can start as soon as they want to once they have reached a new level.

I also like the idea of students reading some of the great articles already posted on the site. Maybe they need to say what points helped them the most or they found the most interesting etc?

A Proof reading task is a good idea too. I think a test might scare some people but proof reading would be not so daunting and yet still show if they have picked up the skills we would hope for in that area.