Unclear, an Arduino could be somewhat like the processor part of a node, though a classic Arduino is not a very good choice. But it sounds like you already have this part.
Microchip is both a generic term for an integrated circuit and a company brand name. That company makes many things (they even bought the company that made the ATmega processors that show up on Arduino). They also make a sub-module that has a LoRa radio and an MCU together under a shield can, and runs a LoRaWAN stack that interacts with a host processor like an Arduino. I’m guessing that’s what you have, and it is a reasonable way to make a node. It cannot be any realistic sort of gateway.
(The Sodaq explorer appears to be a sort of unofficial super-Arduino-compatible with a SAMD21 processor and a Microchip RN2483 LoRaWAN module)
There are lots of threads here on gateway options.