Questions about upgrading from pt9 to 12

Hello... I'm doing this switch and I'm quite scared... I don't exactly know what I'll be going through

My system now is a Mac Pro 1st gen with 10.6.4 and pt9... Next week will arrive here a MacBook Pro retina 15 and I'll have to get pt12

Problem is I have all projects done with pt9, some quite old and I'd like to keep the 9 so I can check in the Mac Pro if everything has been opened right... And if not I can open it in the Mac Pro and export what I need and eventually recreate the project in 12

But unfortunately now I cannot afford to keep the 9...

What problems will I encounter?

Thanks!