the Things Gatway plugs into Ethernet the indoor gateway connects to a WiFi network
both support LoRaWAN and are simple to setup
not with an Arduino as far as I am aware - a lot of computing power is required to support LoRaWAN - Lora point to point is OK
there is a Raspberry Pi gateway HAT - however, the cost of RPi + HAT is probably more than the Things Indoor gateway (apart from the complexity of setting the RPi up)
the MKRWAN 1310 is a good module but looks expensive (£50 in UK)
you could consider for your nodes using ESP32 modules (cost £7 in UK) which have onboard WiFi, Bluetooth Classic and BLE with plenty of IO capabilities - possibly using ESP-MESH for inter node communication
what IoT cloud service are you considering?
I use myDevices/cayenne for both LoRaWAN and WiFi uploads but there are plenty of alternatives (some free up to a set number of devices)
Edit: have a look at decimals-strings-and-lora which an example of a system of nodes distributed over an outside area using Lora point to point for communication