~ I decided to add Bitcoin payment as an option~
Hmm, pretty interesting mate!
Believe me, it feels great when someone does such a new anticipated work related to Bitcoin. OP, I really appreciate your work, but there is one thing in my mind that because of the high fee, no one will pay attention to the small transaction, so according to my opinion, if you used BTC SegWit instead of BTC Legacy so it would be nice. Thus, if your business is big, then if you increase the discount from 5%, there is hope that many customers will be attracted to your shop. Whether they know about Bitcion or not, but when they hear that there is a % discount, they will definitely take interest and maybe in the future they will be able to do research on Bitcion and become your regular customer as well as a Bitcoin enthusiast.
Beside, let me focus a little bit in such a way that, as @mk4 said to check the QR code with time, my opinion is that you should enclose this QR code in a good frame and if at a little expense, print it on a glass/plastic sheet, so that no one will be able to change your QR code easily.