My first post, please pardon me if I’m breaking any politeness rules:
Does current LEDE functionality allow for setting up a secure portion of a router’s bandwidth for open wifi sharing?, ideally, in realtime self limited to the currently unused portion of a user’s internet connection.
I’m no developer...so please excuse the simplicity of my wording.
1.) It depends on what you define as secure.
You could just create a new guest wlan and control the traffic usage over SQM (based on interface and/or wireless traffic).
https://openwrt.org/docs/guide-user/network/wifi/guestwifi/guest-wlan-webinterface
https://openwrt.org/docs/guide-user/network/traffic-shaping/sqm-details
For security this does not much beside isolating the guest wlan from the other (w)lan interfaces. For most people this is what they want to achive.
Further options are routing the guest through a VPN connection to the internet or through TOR for security reason. E. g. if you have people on your w(lan) using filesharing or other "bad" things.
2.) Capabilities and Usage of your router and bandwidth are important too to make SQM useful. I will give only some headwords:
(Moved to "Installing and Using OpenWrt" section. Seems to be a general setup/capabilities question.)
Welcome!!!