Your app will need to be able to use Reticulum. There's a browser already designed for it, called NomadNet, which gives stripped down versiions of things.

For the forward - yeah, basically people can setup mailboxes that will hold messages till the receiver is online. I've got one running on my home system, very easy.

For hardware - depends what you're looking for. If it's just for your phone/laptop, there's some packaged stuff (you'll still need to flash though).

If you want your router to work with LoRA, I used this without issue - it can come with a case. Heltec Wifi LoRa32 V3 433MHZ 863MHZ ESP32 S3 SX1262 OLED Display LoRa Kit for Arduino Meshtastic IoT LoRaWAN Development Board You'll just need to be familiar with a command line to flash - AI can be a big helper here. Basically flash it, put Reticulum on your router, connect the LoRA board via USB and write the interface on the router (via ssh), and you're up! You can make it public and see it on https://rmap.world/.

Got mine on AliExpress, no issues. Also in Europe. One thing that does matter for location is frequency - for Europe it's the 868 MHz.