best laptop review guy i know for general overview.
https://www.youtube.com/channel/UC2Rzju32yQPkQ7oIhmeuLwg/videos
^ that guy will probably release a *very* detailed overclock, undervolt, thermals, everything detailed review. (like a gamers nexus for laptops)
1. You have good ram, meaning no this won't bottle neck your system.
2. The 'boot drive' simply means which drive stores your operating system, and yes, you can install extra games on this drive.
3. On AIO (all in ones) you do not change the water or do any maintenance other than the occasional dusting session to remove the dust in the radiator. Do as often as required.
4. There will be a cap of capacity and speed, however if all you want from your rig is gaming don't worry about it. The amount and quality of the ram you already have is overkill for gaming in the foreseeable future.