Can I offer a course coupon for a free course to select customers? Will it work if I use 100% off for a code?
Yes, 100% off coupon codes is exactly how you can give free course access to certain people :)
I'd also recommend limiting the number of times the code can be used if there's a set amount of people that the code is for.
Once you've created the code, simply send those people the coupon code or the course URL with the coupon already applied (more on that here).