How much time data can be bufferised in FLM before loosing data

In the goal of reducing my electrical consumption, I think at shutting off my adsl modem at night.

Will the FLM keep all measured data in buffers and push all data to Flukso.net at reconnection?
What is the buffer limit?

The FLM will indeed buffer the data and send it all to the server when it's able to reconnect. Try it out by shutting off your dsl modem at night.

If I shut down the ADSL for one month (vacancy), will the FLM bufferize all the data?

The FLM will age your data gracefully. Give it a try.