I’ve managed to get it starting up on boot by following the instructions on https://discourse.osmc.tv/t/osmc-running-custom-script-at-boot/2425 to set up a service using the following:
[Unit]
Description=Spotify Connect Web
After=network-online.target
[Service]
ExecStart=/path/to/script
User=osmc
[Install]
WantedBy=multi-user.target