Installation

‍Do I need to install Nuke.Unreal (and so the Nuke.Targets folder) directly next to my .uproject file?

No. Nuke.Unreal can look for your project file in the sub-directories of its parent folder, or any of the parent folders (except system root ofc).

Plugins

‍Does Nuke.Unreal require all the non-sense that is written in Setting up for plugin development?

No. Nuke.Unreal doesn't impose any of the advanced features on you or your workflows. If your plugin is developed with the most vanilla way and doesn't require any extra steps to get distributed on Fab then you don't need any of the plugin development facilities Nuke.Unreal may have. (also good job for keeping your plugin lean!)