Do I really need a subscription with 8 cameras?

You can connect up to 15 Arlo Ultra 2 cameras to a single Arlo SmartHub or base station, such as the VMB5000, VMB4540, VMB4500, or VMB4000. This applies regardless of whether you have an Arlo Secure subscription. However, note that only 5 cameras can stream simultaneously from a single base station or SmartHub. To stream more than five cameras at once, you would need to use multiple base stations or SmartHubs.
kb.arlo.com

If you have multiple base stations or SmartHubs, you can stream up to 15 cameras simultaneously using the Arlo Secure Plus plan, provided none are connected to a base station. Alternatively, you can set up multiple Arlo accounts, each linked to a separate base station, and grant access to a master account to view all your camera feeds under a single login.
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Keep in mind that Arlo recommends a minimum upload bandwidth of 3 Mbps per Ultra 2 camera. Therefore, for 15 cameras, you would need a total upload speed of at least 45 Mbps to ensure smooth operation.
arlo.com

In summary, while you can connect up to 15 Arlo Ultra 2 cameras to a single base station or SmartHub, only 5 can stream simultaneously without additional setup. To stream more than five cameras at once, consider using multiple base stations, SmartHubs, or Arlo accounts, and ensure your internet connection can handle the required bandwidth.

yes on the application. Please note that the Arlo Ultra 2 only connects to WiFi via the hub supplied with it. The camera cannot be connected directly to your wifi, without going through their hub.