Hi again, @Emmanuel-W.
Going through your questions:
(smart grid)
This allows your utility company to partially “take over” your HP controller in order to match regional power supply and demand. It isn’t available where I live, but it might be in Belgium.
Your installer should have supplied rubber feet to your Outdoor Unit “…to reduce noise and vibration.” (Installation Manual). Especially important if roof-mounted I would have thought. Did he?
Well, the simple answer is to have a high night-time setback, but this is not necessarily the lowest cost option and may not even be feasible with your heat pump capability (see the House Thermal Inertia and Roomstat Setback (some cautionary notes) topic). I don’t use the programmer in the Samsung remote controller for space heating on-off timings (I have a third party roomstat for that) but it appears to have the necessary functionality.
Your other option is to enable Quiet Mode. (You can do this at the remote controller, including setting up which time spans at which you want it running quietly.) This mode restricts the compressor to ~60% speed. So it runs quieter, but takes longer to do anything (like getting your house warm in the morning).
This is where it gets a bit complicated, and it’s all down to your FSV#2093 setting. Starting from cold (e.g. after night-time setback finishes), if #2093 = 1 the heat pump will run at full speed until the LWT approaches the Water Law target, then slow down to minimum speed and stay there until the Roomstat is satisfied. This may result in LWT exceeding the WL target, but it won’t actually stop the compressor until your room reaches roomstat setpoint. But if #2093 is set 2-4, when LWT reaches WL target it will not only slow down but actually stop the compressor (even if the roomstat setpoint has not been reached). Once the LWT has fallen by ~2K (the water circuit is still operating so is removing heat via the radiators) the compressor will start again and cycle in this way until the roomstat is satisfied. (The only difference between #2093=2/3/4 is how the water circulation pump operates - off, on or cycling depending upon whether the roomstat is satisfied).
Yes if your Water Law settings say LWT should be 40degC for a particular outdoor temperature, you can add or subtract up to 5degC to/from this number (i.e. have LWT = 35 to 45degC) if you need to adjust things temporarily (e.g. a cold easterly wind is keeping your living room unacceptably cold one day).
Not unless you have Cooling set up as an option (needs a second roomstat and setting up a separate Cooling WL on the FSVs).
Whether you run your HP on (day) and off (night) or continuously depends mainly on whether it is keeping your house comfortable. Conventional wisdom is that unless you have a really cheap TOU tariff it doesn’t make much difference to the economics how you run it. The undeniable optimisation factor is minimising your LWT consistent with comfort 
.