All the "Send-to-Kindle" (STK) content should all be archived on "the Cloud" unless you deliberately turned archiving off. Those books/"personal documents" should all have reading position, notes and highlights synced to your Amazon account that you've registered that PW2 to.
You can check what STK content is saved to by going to
www.amazon.com/myk, logging in and setting the "Show" filter on "Your content" to "Docs". Or you can do the same thing using any of the Kindle apps.
If all your not-from-Amazon books/content is there you will be able to just download all those books on your new Paperwhite once you register it to that same Amazon account.
If you don't want to have to download all those books couple at a time you could instead just copy the whole "documents" folder (that is where all the books and notes/highlights are; both paid-for and sideloaded/STK/converted from epub books) from you PW2 to your PC, and later Copy that folder to you new Paperwhite.
Only one thing you have to keep in mind: All of the Amazon-bought books that you had in that "documents" folder will not be able to open on your new Kindle (because DRM applied to those book is device specific), you would have to first delete them one by one (as you discover them, by trying to open them) and just re-download them from the cloud archive. Your Send-to-Kindle content doesn't have DRM protection applied so the same file can be used on any device, by simply copying it to new device.