question

In light of the forum rules with regards to system design, I can only propose reading up on the ESS and generator start stop documents on the Victron website.

Some basic tips however are. The Quattro range or even new Quattro-II will allow both the grid and generator connections. If it is a Multiplus-II, you will have to implement a transfer switch, which can be automatic or manual.

Maybe look at the Multiplus-II, Multiplus-II GX or even the Easysolar-II GX depending on whether the 4.4kW (5kVA systems) will suit the requirements. If you only occasionally exceed the max output, it is not a problem as the ESS system will just top up the shortfall from the grid. (There is so much more to a system design than a diagram, so you may want to consult with a Victron installer/dealer.)

The differences between the above Multiplus-II models are the level of integration of inverter/charger, GX and MPPT devices in a single system and the all-in-one Easysolar may just do the trick, but you can find all that on the Victron website.

The "no power limit when the grid is used" will depend on the peak loads when in passthru mode and whether you have loads on the ACOUT of the multiplus. In essence, there is a limit determined by the model and transfer switch rating. This can however be overcome with a grid parallel installation, which only requires a connection to the ACIN.

Finally, the ESS assistant can be programmed to charge to a schedule, disallow feedin etc. which are all explained in the documentation. Do ensure that before you buy the system has a G98/G99 certificate (UK) or equivalent to allow it to be connected to the grid wherever you are.