New MacBook Air - iTunes + iPhone Workflow Help

Just got a new Air and have a situation I can't figure out.

1) I have 60+ GB of music on my OLD MBPro
2) I'd like to transfer 1/4 of that music to my Air - not all of it
3) My iPhone is sync'd with my old MBPro
4) I can't add music/videos/anything to my iPhone from my new Air (iTunes prompts me to delete everything on my phone)

I believe it's not possible to sync an iPhone with two different systems, what's annoying is that you can't even manually drag music from the NEW system to the iPhone. So stupid, typical Apple BS.

Since my NEW Air will be my primary system, I'd like to:

1) Transfer SOME of my iTunes library to the new Air
2) Sync my iPhone with my new Air but not lose my content on the device

What are the best ways to do #'s 1 & 2?

Thanks in advance

Anyone???

1: Connect your old MBP to your new Air. Air sharing even allows this without cables. You can select and move files as you need to.

2: Doesn't work. You can sync with one computer at a time. You can select to have the new computer not sync Apps, or on the new computer simply download the items from your purchase history within iTunes.