No. Static QR codes never expire. The data is encoded directly in the image — it's a visual representation that works forever. Only dynamic QR codes (which redirect through a service) can expire.
Yes. Download the PNG and use it anywhere — business cards, posters, menus, packaging. For best results, ensure the QR code is at least 2cm × 2cm when printed.
Make sure the network name (SSID) and password are exact, including uppercase letters. WPA/WPA2 is the most common security type. Some older phones need the network to be in range before scanning works.