Here is a script that will autostart Syncthing (download ARM binary manually and put in non-RAM location):
sudo -u USER nohup /LOCATION/syncthing > /dev/null 2>&1&
“sudo” and “-u USER” can probably be removed as “root” is likely the only SSH user in LEDE, like in Tomato.
In Tomato there is a cron area and a “run at startup” section in the GUI to enter any given commands or scripts. Look for something similar in LEDE to put above script in. If LEDE has a home folder that isn’t in RAM one can also put the script in a file called “/home/USER/.profile” or “/root/.profile” (for root user) and it will run at every SSH login (which is basically almost equivalent to auto-starting).
If still need help auto-starting script on LEDE post here: https://forum.lede-project.org/
They are very helpful.