One idea is to show them to this site here -- though only allow the ones you know won't troll to come.  This way, you all have a way to commuicate, not only with yourselves but also with an experienced community as well.

I would say go to a teacher and ask just how you can get one started -- then advertise!  Don't make it sound like 'Nerd Stuff' -- show pictures of awesome games like Starfox 84, ROL3, Trio and Niko: Falling etc., and also show some trig solvers and graphers as well -- appeal to everyone!  Show why calculator programming is the rage -- yuo can do it anywhere, it's much easier to set up a coding environment on calc rather than on a computer, and you can learn from this experienced community so you can start making games fast! 

good luck with the club -- advertising is the key to success

I'm thinking about starting off things with a test to know who I'm dealing with. I'm leaning towards having the questions be all over the place. Thoughts?

I am starting one too.  It will be a first semester only club though.
I have a teacher too so it is "sponsored" by our school.
We have a Chess club/Rubix cube club, that is combined together.  Calc club will be joined with them for the 1st 1 or 2 years.