Only 4 connections are needed. The 3.3v, GND, TX and RX. I use GP0 and GP1 of the Rasbperry Pi Pico board. Image and simple micropython code below. Perfectly fits on the small breadboard 
from machine import UART
from machine import Pin
import time
decoded_data = ""
led = Pin(25, Pin.OUT)
uart = UART(0, 115200) # use RPI PICO GP0 and GP1
## CODE TO SETUP RAK4200 - OTAA, Class, Region, keys##
uart.write('at+set_config=lora:join_mode:0\r\n')
print("set to OTAA")
while(decoded_data != "OK\r\n"):
data = uart.readline()
decoded_data = data.decode('utf-8')
print("OTAA done!\r\n")
decoded_data = ""
uart.write('at+set_config=lora:class:0\r\n')
print("set to Class A")
while(decoded_data != "OK\r\n"):
data = uart.readline()
decoded_data = data.decode('utf-8')
print("Class A done!\r\n")
decoded_data = ""
uart.write('at+set_config=lora:region:EU868\r\n')
print("set to EU868 reguion")
while(decoded_data != "OK\r\n"):
data = uart.readline()
decoded_data = data.decode('utf-8')
print("EU868 done!\r\n")
decoded_data = ""
uart.write('at+set_config=lora:dev_eui:00396E15EFDF4648\r\n')
print("set to DEVEUI")
while(decoded_data != "OK\r\n"):
data = uart.readline()
decoded_data = data.decode('utf-8')
print("DEVUI done!\r\n")
decoded_data = ""
uart.write('at+set_config=lora:app_eui:70B3D57ED0038D62\r\n')
print("set to APPEUI")
while(decoded_data != "OK\r\n"):
data = uart.readline()
decoded_data = data.decode('utf-8')
print("APPEUI done!\r\n")
decoded_data = ""
uart.write('at+set_config=lora:app_key:7B2BD89FAAF26CBDC694257F7EC92D1B\r\n')
print("set to APPKEY")
while(decoded_data != "OK\r\n"):
data = uart.readline()
decoded_data = data.decode('utf-8')
print("APPKEY done!\r\n")
## END OF SETTING UP ##
## TRY TO JOIN THE NETWORK!##
decoded_data = ""
uart.write('at+join\r\n')
print("joining!")
while(decoded_data != "OK Join Success\r\n"):
data = uart.readline()
decoded_data = data.decode('utf-8')
print("join success!")
while(1):
led.value(1)
uart.write('at+send=lora:2:1234554321\r\n')
print("LED ON")
time.sleep(5)
led.value(0)
print("LED OFF")
time.sleep(5)
