New laptop, existing iPad and snyc issues

Ok. New laptop installed. iTunes installed. All apps transferred. iTunes music and other sourced music available in iTunes. All my PDF files in iTunes 🙂

And yes the new iTunes is authorised on my Apple ID.

But...

I need to sync my PDFs and I get "The iPad is synced with another computer..." do I want to "Erase and Sync".

This leaves me with questions:

Why can't I migrate to the new laptop?

This is from Apple, it should be easy right?

Will "Erase and Sync" mess with my layout (experience tells me yes)?

My iPhone has my music, so it's going to be worse when I move it over right?

Important items to note. All items (music,apps,pdfs,...) are on the new laptop, but I know where everything is on my iPad/iPhone and I don't want it to change.

Thoughts and advice appreciated.

Bruce