Great to see that you want to attempt something like this.
Chances are, using meetup won't work, as most township people won't be familiar with it.
You'll need to use offline advertising and maybe create a "maker-space" where people can come together and "do things".
The only issue you'll face is likely theft of equipment. Although crime is a reality in SA, it is even more rampant in townships, so you'll risk losing equipment, unless you can secure the maker-space into a fort-knox-like structure.
Also, I understand that Project Isizwe is aiming to provide free wifi to underprivileged areas, so utilize that as an enabler for your project.
The last thing is interest. I personally don't think many township folks care for Linux, just like how most MS-Office/general users don't care for the OS underneath.
Based on that, you may have more success at underprivileged schools. A grassroots effort to just show the school and pupils that Linux is exactly the same as Windows (but free) might work. Linux alone won't work either, so maybe a general hacker space will be better.
In terms of what you can do to advertise, word-of-mouth and a nice big board saying "LUG here" will work for now.