@slarti: Very interesting use case here
I don't know the ZWAVE controller - as a premise - but:

Is there any way for the ZWAVE to report an unsolicited status of all/some sensors, like for example if you have a temperature sensor attached to it, is it possible to be notified by ZWAVE about a change in the temperature or you have to periodically issue a polling wget?

Apart from wget command, is there any other way to change the status of devices (ex. some impulse on the device itself, switch, potentiometer...)?

Issue here, for representing devices status, is to be as much real-time as possible, thus triggering a beecon status update every time it is necessary (and avoid timered polling on all devices to know their status - what timer period? how much battery will this consume?)

How can the ZW initiate a communication with the N900, if possible?

The DIM part is not as much difficult as it seems on first sight.
In QBW you can sense the tap/click position on a widget and return a different exit status value which will be converted into an image; precision and tolerance is indeed up to you ... you want to manage 30 different intermediate levels you just create 30 different images and alter some divider in the script
I'll follow up on this as soon as I receive some of your feedback on the matter

Bye.