Hi
I don't know of a stylus for the Playbook but you can use your blackberry smartphone as a remote for it and type on the keyboard, or you can use the new Keyboard/Case that Rim as just brought out for it -
RIM Introduces the BlackBerry Mini Keyboard for the BlackBerry PlayBook Tablet
As for a note taking app, I would recommend Groovy Notes as it is good at organising notes and can back up to dropbox.
I have a list of my Top Playbook apps on my blog -
My Top Apps for The Playbook
Hope this helps