It would be great to offer the course for free, and totally agree with you to charge a refundable deposit if they attend all 5 weeks. Perhaps the cost of the deposit should be denominated in SBD to get them in the Steemit think.

And my tuppence worth

1. If your focus is to promite Steemit as a blogging community and earn some cash on the way, I wouldn't talk about cryptocurrencies and blockchain in week 1 just yet, maybe in week 2. In week 1 maybe talk about searching for posts and tags, and how to follow people so they can do that themselves during the week, basically to keep them active on Steemit

2. Need to emphasis this is not a scam. Charging, even a deposit for a course, so you can earn money just by writing in the long run, still sounds dodgy to many.

Good luck!