Photovoltaic system: Costs, saving potential? - Experiences?

That should be a bit more than 10kWp?
At first glance, the offer looks well calculated in terms of price/performance.
Never heard of the module manufacturer.
BYD is known. They are supposed to run quite solidly.
I have learned: Fill the roof as much as possible (sensibly). Keep the storage as small as possible.

The mounting frame are the aluminum rails on which the modules are screwed. Without them, you can't proceed.
The ladder scaffold should be unnecessary since you already have a scaffold.

Modules are assembled in Austria, but the material comes from China – so Chinese modules with a European sticker. I have no experience with them; they are probably rarely found here.
BYD is almost standard. You have been offered the cheaper version.

Price/performance is absolutely fine in my opinion.

Whether SolarEdge is really needed depends, in my opinion, on the roof conditions and orientations.

SolarEdge needed?

One of the most important specifications is missing here: What charging and discharging power do you have in the system? The charging power determines how fast you can charge the battery when the sun is shining; the discharging power determines how much energy you can draw from the battery at a given moment if needed. Example: You are cooking on induction and have a few other consumers on. You need 7 kW power at that moment. The battery is full; the photovoltaic system delivers no or insufficient power (dark, cloudy...). With a typical discharging power of 3.5 kW, you are effectively buying power even though there is enough energy in the battery. I would pay attention to that.

A hybrid inverter with 2 MPPT inputs should be sufficient if you don't have major shading problems.

I would go for a compact and tidy all-in-one device; I have this one myself with 8 kWh battery capacity and 8 kW charge-discharge power in use. With more storage capacity, the device grows about 50 cm taller. I can buy batteries any time and plug them in like a drawer. Software updates come over the air, so I am well prepared for a long service life and future applications. The heating rod is still lying around; I should connect it sometime. Preparation for a charging station with surplus power control is included, but I still drive a combustion engine. Whether I want to control household appliances, I don't know yet. (Image should be rotated)
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One of the most important pieces of information is missing here: What charging or discharging power do you have in the system?

Which device do you have? Do you know the manufacturer and type?

At 50 volts, so just under 10 KW output power.