How likely is it that anything will happen to my phone (it gets bricked etc)?
Very unlikely. You can revert to the stock OS.
Will everything work on the phone (Profile Switching, Google Services incl Apps like Snap and TikTok for work and also YouTube and many others)?
The things you listed will all work. The Google services compatibility layer supports most functionality, but there are a few exceptions. Screen mirroring does not work. Tap to pay with payment apps like Google Pay does not work. Apps that use the Play Integrity API may refuse to work on GrapheneOS. GrapheneOS fulfills all the security properties of the stock OS. The Play Integrity API however only verifies devices running on the stock OS. This is mostly used by some banking apps and pure security theater. You can find a list with the compatibility of banking apps here: https://privsec.dev/apps/banking-applications-compatibility-with-graphheneos/
GrapheneOS has some security features that can rarely interfere with apps such as blocking native code debugging (also used by some apps like some banking apps as security theater or as a weak attempt to hide what they do from you). You can disable these in the settings on a per app basis. Generally 99% of apps will just work. But be aware that things can change in the future and Google might add functionality to Google services that apps might decide to depend on and which GrapheneOS cannot or will not support. But you can go back to the stock OS anyway.
Is there anything I should be aware of before installing?
Make sure you get a device with an unlockable bootloader. Carrier locked devices may have a bootloader that cannot be unlocked. These are sold as part of phone plans. If you buy a new device without a contract the bootloader will be unlockable. On the second hand market these devices can mix. After carrier locked devices have been paid off they may get carrier unlocked but the bootloader can remain locked. Those devices might be sold as unlocked but their bootloader may not be unlockable. If you buy used make sure the device is truly unlockable or you have the option to return the device.
Can I install apps from Google Play?
Yes.
Will the Camera work normally?
The default camera app is very limited and cannot use the camera hardware well. But you can use Google Camera just like on the stock OS.
Is GrapheneOS more laggy than normal android? Can it be used for lightweight gaming?
App cold startups take slightly longer due to a hardening features. In practice this is barely or not at all noticeable. YOu can use GrapheneOS for gaming.
Is there a way to "fake" root access for the apps that need it? Even if it's a bit more technical?
No. You can fake to apps that they have the normal Android full filesystem permission while only allowing them access to selected folders using the Scoped Storage feature, but you cannot fake root access.
Which of the listed phones would be the best and does it make much of a difference?
Depends on your requirements and budget. The generation 8 devices have hardware security feature improvements, but any supported device is fine as long as it receives full security update support. Make sure that your device gets guaranteed official security updates for as long as you plan on using it (important for firmware updates), GrapheneOS will fully support the device until then. Budget wise the 7a is a good option as it gets security support for another 4 years and is comparatively inexpensive.
Read the FAQ and usage section on the site.