I want to set different user and passwd for web and ssh, respectively when I build LEDE firmware. what should I do?
Maybe a lot of changes you need to do, or try luci-ssl as web interface.
At build I don't know, but this may get you started:
The idea is to create multiple users in Luci and use one of them that will be denied ssh access. Then you could create a non privileged user to access ssh only.
Yes, thats a very good feature to integrate on LEDE. In most scenario, some users may want to monitor bandwidth, while the network admin would not want to share SSH password.