Hi, @steve!
It’s not unusual to get warning messages when working with yarn. These can usually be ignored. That said you seem to be getting more warnings than usual.
Could you give us more information about the environment you are developing on? What have you tried to fix the issue?
As an aside, when you choose Bootstrap as your framework you can chose no when asked to overwrite the files (because Bootsrap is the default framework - Are you sure you want to overwrite the following files?).