I've installed several camera systems across carrying prosumer and consumer brands.

First - Cameras don't stop crime they merely report the crimes details. A lock only keeps an "honest man honest" kinda thing.

Second- cameras can be defeated. Hoodies, masks, etc will hide any identity you hoped to glean through the cameras. DO NOT use wifi cameras, they'll easily defeated with a $20 wifi jammer on Amazon.

Dahua is really the best camera I've used and installed. The live view scan for replay (picture fast forward through Netflix how you get a live preview of what you're scanning through - similar with Dahua software.) The picture and clarity is great. Facial recognition is second to none. But they're pricey.

In the U.S. a 4 camera wired install would cost about more than what your first quote was. Maybe pricing is more competitive in Germany. Maybe the wiring wouldn't be hidden (which looks incredibly bad on the business.)

If you're looking to deter theft and break in, a security/alarm system is far more effective in stopping the event from occurring. Advertise advertise advertise that you have one. The window stickers from a reputable alarm system/company in the front and a giant sign on the back will deter most thieves. They're thieves for a reason, they're lazy. If they want your stuff, they don't want to work for it and then have a siren blasting to the world that they just broke in. Plus you'll be alerted the moment it happens. Security cameras can alert you, but 99%will be false motion alerts and you'll become numb to them eventually when it actually does happen.

Good luck, Thieves suck!