This is a great summary of the current issues with the QSesame plugin and the Sesame API right now. I've noticed all these issues too--some of them can be addressed and some are more challenging.
One thing I've been looking into is making the plugin a Homebridge "platform" instead of an "accessory". The benefit to this is that it would 1) allow dynamic loading of the device ID for the serial number 2) allow for multiple Sesames and 3) is more realism to names changes on the Sesame. I'm still waiting on my wifi access point and I might invest more time after I receive it.
The notification thing is super annoying. It's actually a limitation of the Home app and there is currently no work around except to disable notifications on each individual device.
The look state problem is actually a combination of problems. The big one is that the Cloud API is lousy at detecting manual lock turns. The other problem is there isn't a good way to "push" updates tfeom the Cloud API to apps like Homebridge. I've been thinking about "fetching" the status every 15 seconds or something (and then pushing to HomeKit), but this could put a pretty big strain on the CANDY HOUSE servers--and I'm not sure if there is any rate limiting in place.
The errors you've posted about happen to every Homebridge user. It's caused by a dependancy they use, you can just ignore it.