You can make the Aqara work better by careful planning of your Zigbee network and adding specific Zigbee repeaters only, like IKEA Trådfri outlets and repeaters, but it's easier to just buy Samsung Multisensors. But for the stairs, I agree that motion sensors with the @mike.maxwell method is probably more what you need.
If you're interested in linking hubs, there's lots that can be done. I use an Aqara HomeKit hub with Homebridge to link Xiaomi sensors. That gives perfect results, but you have to have Apple products. You can link a specific Xiaomi hub as well using Mi Connector. That will give you direct access to devices like temp/humidity sensors and then you can use them for reference levels in rule machine rules.
SharpTools is nice. Not sure this is what you're looking for, but the built-in Hubitat Dashboard can be customized and there's help here on that. I'm certainly not versed on CSS but others are.
