Set it up myself, mostly. Some specific tasks like bringing three-phase power to the garage and hooking up the breaker box I did with an electrician. But installing an additional circuit inside the breaker box, or putting new conduit up, is easy to do safely yourself. Pre-wired breaker boxes can be configured online and are cheap.

The battery is 16kWh. Effectively around 14kWh, since you never fully discharge. LiFePo4, so no chance of spontaneous combustion like other battery chemistries.

I'd say the months Nov→Feb are tricky, although since I have quite a bit of excess solar capacity there are even in December plenty of days where the battery pulls me through the night.

Charging/discharging from/to the grid is possible, since I have a retrofit inverter (AC to battery), but not doing it yet, have to do a bit more research (dynamic pricing, tax is >50% of the kWh price in NL, etc).