Hi Andy,
Yosemite is really a mature and troublefree system, but needs more resources. If you have just 4gb of Ram (or less), you should upgrade. Bevore installing Yosemite perfom the both harddisk checks (volume & authorisation) in the disk utiliy.
Regarding the broken IOS sync:
It might need a new pairing between iTunes and the IOS device via USB connector. Make sure that check checkbox for the Wlan sync is active.
If it still doesnt work, it might be caused by the IOS device (fragmented memory). Usually it will work again after closing all open apps. Then shutdown the IOS device by holding the switch ON pressed until the slider pops up. Wait until its completely shut off. Then switch it on again and gibe it another try.
Remark: this oddity occures once in a while especially on older devices with less Ram (I am not talking about the size of the Flash!)
Best regards
Kurt


M3W willow green,Triumph T100,KTM LC4 Adv./Freer.250R, RD250/RS125DX, Alpine A110
Kurt