Can access to my icloud be limited to only me

That's a very broad question since iCloud has many parts, some of which can be shared if you so wish. For example:

Share iCloud+ with your family - Apple Support

Can you narrow down your area of interest or concern? Nobody can see your iCloud data unless you choose to share it.

Yes , unless you don't share your Apple ID account credentials with other users and they can't sign in with same Apple ID and password on the same network with their devices see Keep your Apple ID secure on iPhone - Apple Support

For more information about best practices, see the Apple Support article Security and your Apple ID.

They should sync if you have Notes syncing turned on in iCloud settings.

Change which apps sync and store data with iCloud - Apple Support