Running both Snow Leopard and Mavericks, MBP 2009

I have a mid-2009 MacBook Pro (4GB RAM, 2.26 GHz, 160 HD) that is currently running Mavericks (10.9.5). I’m having issues with iTunes (12.3.1) finding my library since I copied files from my Time Capsule to an Ext. HD. I’ve researched and followed directions, but my library, though on the disk, can’t be found and it also doesn’t want to find it on my Time Capsule either.

I thought I’d downgrade back to Snow Leopard, but Aperture (3.5.1) needs Mavericks. Now I’m thinking of running both Mavericks for when I need to use Aperture, and Snow Leopard for iTunes and most everything else since it seemed to play nicer with my MacBook.

How would I best go about this? Both my Aperture and iTunes libraries are on a 4TB Ext. HD. Everything is backed up to a second 4TB Ext. HD. I’m a newb when it comes to this stuff. I’ve read that "running two partitions or multiple drives is the best way to handle this and provide the most compatibility as opposed to virtualizing.” Someone also said I could "Boot off the DVD and use Disk Utility to create a new partition on the internal drive. Install Snow Leopard there. You can then boot into which ever OS you want.” I’m assuming that means either two partitions on my HD or one OS on my HD and the other on the Ext. HD? If so, what would be better? Could I place Mavericks on the Ext. HD and Snow Leopard on my MacBook’s HD?

To complicate matters, I live in S. America where Macs are rare. In my city of 1 Million I only know of one Mac tech. My Spanish is good, but I don’t talk computers well even in English and am looking for advice or ideas before having the tech do anything, thinking he may just do whatever is faster and more convenient for him. I’m also wondering if I can do this myself, since I have Time Machine backups going back to before I installed Mavericks, but would probably have a tech do it anyway. Just want to know what specifically I would ask for him to do.