I am happy to share my experience with the Home Hub Pro, having installed about a month ago. I too have 10 cams installed of various models (all but 1 are battery/solar) and 2 more yet to install. I have split the cams - 4 under the Hub Pro to test, 6 (1 dual-lens, so technically 7) are still independent and viewed using the same reolink app under which the Hub is viewed. This applies to users accessing cams from iPhones, MacBooks, Windows 11 desktops, and more.

1. Dunno, I have no 4G cams, nor am I looking to get any.
2. I believe so, according to the Hub Pro's camera source list (1-24), and the product page on the reolink site.
3. It is possible to have corruption affect performance (on anything.) That applies across the board and I'd like to think reolink has error correction/continuance code by design. * As for accessing the recordings: I originally couldn't access any recordings under the Home Hub Pro until after I updated my Reolink client app to v8.17. Before the update I always got a message stating "This device does not support recording" even though the HDD on the Home Hub Pro (HHP) was clearly filling up. Just make sure you're up to date on you app and firmware...
4. Not that I can tell. I haven't removed an SD card from any cameras under the HHP yet to determine status of local recording though. Sorry, holiday bug put me down for a couple weeks. The "Record" function was also missing under any Hub camera's settings prior to the 8.17 client app update. Either way, I don't see a software path to view the camera's local SD card once it's moved under the HHP.
5. Factory reset required physically at/on the camera. (pin-hole tool suggested)
6. Not all but a lot. Some things that concern me because they are missing are:
   1. No info stated by Reolink that I could find informing a client update was needed to correct issues like "Info" tab only showing HHP data and not camera data, inaccessible recordings, etc. Once updated though, several issues were indeed resolved.
   2. As stated in #4, access to &/or control of local storage physically installed in the camera once moved under the HHP seems missing with no supporting info to say if it's even functional.
7. I believe this is possible by design but have not tested it myself yet. There are settings under Network for Server and HTTPS settings. I believe it will allow access via both paths. Can't say about simulcast across more than one platform at a time though.
8. If there's a way to do this, I can't find it. There's a "Push" option for each camera where you can schedule alert times but no way to customize the alert itself.
9. There is User Management under System in the Hub's Settings but when I attempt to add a user (logged in as Admin) it always returns "Failed" with no indication why, only an "OK" button. As for controlling what any user can see, I've not been able to get that far...

Overall, I'd say this unit is close to ready for prime time and has room for improvement. Outside of centralizing recording storage (and providing a larger storage medium - which might be moot since >1 camera is filling the space), I'm not sure the value proposition is great enough to justify the expense. My biggest beef overall is, and has been the slow access and response time overall with Reolink products. Whether it's recording or simply viewing a camera from a triggered push notification, by the time the camera begins recording or displays live on a device from having been triggered, whatever caused the trigger is usually gone from the frame, and more times than not, the object tracking ignores the subject's movement/doesn't track it, no matter the sensitivity level settings. This is beyond the scope of the HHP though, and seems a design limitation with Reolink camera products in general; esp. those that are battery powered (which may be part/all of the reason for such delays, but they seem to occur on my POE PTZ camera too...) - which can make sense to preserve battery, but also flies in the face of the entire purpose of a security camera in the first place.

In my experience, Reolink doesn't publish any reviews that are below 4 stars on their site, so using that as a litmus test is superfluous.

Hopefully this helps you or someone else (if it survives...)
Cheers,
C