Thanks for the suggestions; considering my cost, I will consider doing only 3% off for customers paying with Bitcoin; I think that will make them happy. Also, with that, I think I am going to edit my display and indicate 3% off for payment in Bitcoin.
You know best how much discount you can allow yourself, but if I were you, I would consider rounding that amount to 5% because it will have a much better effect on people psychologically. Sometimes you need to put yourself in the shoes of the buyer in order to be a good seller

Already, I am working on printing some flyers and stickers to distribute within my area.
This is surely something that will bring you new customers, because advertising is the key to any serious business. If people don't know that you exist and that you offer payment with Bitcoin, you can only hope that someone will come to your store by chance.
But it is business he is running, and it would be hard if he'd earn less. Wearing you customers' shoes is a good idea but consider the side of the merchant. What he is doing is simply a trial of adapting this technology which is definitely great but if it would sacrifice the goal of his business, then that would be a bad thing. Things must be fair on both ends, as what I am trying to say.
Thats really great to hear and feeling proud that, our neighbors even each and every common mass around us is using Bitcoins. These same Bitcoins were frowned by the same people few years ago. Nevertheless my only doubt is that, is Bitcoins legal in your country? If yes then do you pay tax on it? As you are using it in accepting payment. Also if Bitcoins arent legal, then publicly promoting about accepting the coin, might make you to face some legal issues. Keeping all these apart, I really loved that you made the A4 sheet print out yourself and allowing customers to use Bitcoins. Keep us updated about more of your journey.
The usual setting in countries is that, cryptos are allowed to be used but are not supported or being promoted by local governments to the public. They have their own reasons which surely involve issues regarding taxation.
Going back, many small businesses have tried accepting this technology as a mode of payment but eventually most of them stopped. Losing in this industry during down times, even if it is temporary, won't be sustainable to a business because funds need to circulate in order to run the business while maintaining crypto investments. So I hope OP would do it right this time.