Resolve 12 quits when importing quicktime?

Hello,

total noob (audio dude) here. I installed Resolve 12 on my MacPro and it opens just fine, but when I try to import footage (mostly quicktime or mpeg4) the application simply quits.

The system guide states that Resolve requires 10.10 or later, but in the App Store 10.9.4 is given as minimum requirement?
I suppose I could update my OS to Yosemite, but it would require some paid upgrades for other software I use. It is something I'd have to do eventually, but I'd prefer to hold out for now.

Also, my MacPro 4,1 has a humble NVIDIA GT120 and it seems that card is not supported? I wonder if it would make financial sense to upgrade the GPU on a seven-year old machine?

system specs:
Apple MacPro 4,1 | Intel Xeon W3520 (2.66GHz quad) | 12GB RAM | Samsung 850EVO 500GB (in OWC Accelsior S PCIe adapter) system SSD | NVIDIA GeForce GT120 (512MB) | OSX 10.9.5

I do not intend to do heavy stuff, just some basic HD editing for Youtube etc.

And finally, I know my 2013 MacBookAir is not on the supported machine list, but would it suffice for said basic stuff?

Thanks.

your gpu is severely underperformed, resolve is a GPU hungry monster