I think you're right on the ball there with what you have. I wouldn't present too much structure for the students because this type of activity in itself needs to be free.
I give students blank sheets of paper and they have to start by writing in the theme (rather large) anywhere they'd like on the page. They can build off of the theme in any manner spider webing out from the main theme or growing up, out, down or around. This is their creative/brain storming sheet. Which they enjoy designing and illustrating.
On a separate sheet of paper they do all of their work with the words. In the end you have 2-3 sheets of vocabulary and vocabulary in use.
It's a really good exercise and you'll see loads of variations from the same student.
I've found that structuring really dampens motivation for the next go around. By letting it be free and loose, the students have something to look forward to.
I have several examples prepared that show the students some ideas of how they can create their theme vocabulary pages. This gives them some ideas and for the less creative, they give them something to copy.
That's my 2 cents anyway. I didn't read the original post you're speaking of and they might have had a better plan.
Mark
www.mes-english.com