To answer your last question: none of these products need an Aqara hub.
But regarding hubs and future smart home upgrades:
The G5 Pro is a camera hub, which means it’s a hub on its own. And it’s Matter-compatible, so it’s a great value for money.
So if you plan buying it, it can be your first Aqara hub. In the future, if you feel like upgrading, you can just buy another/newer Aqara hub and you can migrate all your devices to the new hub with a few clicks in the app.
But generally a hub enables you to use Zigbee firmware on Aqara devices, and usually this Zigbee firmware has more features than Thread firmware. And automations in the Aqara Home are more sophisticated and capable than HomeKit automations.
So the G5 Pro should future proof your smart home, and if you plan on buying more Aqara products, it can be used as a hub.
As advised already by @cezary806 you already will have a hub with the G5 Pro. If you can, I’d suggest PoE as I’ve found cameras in general work better over Ethernet than WiFi. (this isn’t an Aqara thing, but a multi-vendor thing). They send a great deal of data and so are more likely to have data collisions, which is something that WiFi does not handle as well as Ethernet.
I can’t comment on the U400 as I’m in the UK. However, as you want Apple Home Key I can say it’s a great combination. I have the U200 and G400 with the power running both the G400 and the U200 keypad.
In your case, it doesn’t matter with what you’re implementing. However, sometimes the zigbee firmware does offer more capability than Matter. However, as Matter matures I expect that to change. If there is something you want though, in HomeKit, Aqara provides the ability to expose it to Apple Home via some very clever methods.
There is a difference between what you need and what it is recommended.
I also have both, a good and fast WiFi Mesh network but also some devices connected via LAN cable and POE powered.
And is if comes for what you need, both are fulfilling their purpose, but if you ask for recommendations, I also clearly vote for POE connected and powered devices over WiFi connected devices.
I’m afraid I disagree. I have a good WiFi mesh. No matter what you do, you will have data collisions. It’s better with later versions of WiFi, but it still happens and Cameras are very Data intensive, so are more susceptible to those collisions. The more Cameras you have, the worse it will be.
So, yes, a modern WiFi mesh can possibly do the job, but Ethernet is better.
I second this, especially given most cameras use the ol’ reliable 2.4GHz WiFi, which usually hosts most of the, let’s say, casual traffic (only data intensive clients close to the AP, like laptops and phones, will switch to 5GHz). And coincidentally, the 2.4GHz also is shared with Zigbee.
All those facts considered, it means the WiFi streaming will be regularly worsened by interference (streaming just pushes the packets through the network without making sure they are delivered, so there may be many dropped packets). So even a 10Mbps Ethernet will be better than vastly congested 2.4GHz wireless channel.
I agree with the others, no Aqara hub required at this time with your setup. See how you like everything, then if you want to advance your automations/setup further add a Aqara hub into the mix. Thanks