I'm having the same issue(s). However, this has been going on for me since iOS 7. I get stuck at "Waiting for items to copy". I've pulled the plug before when this message appeared for more than 15 minutes, but, that totally screws up my iPhone. Missing songs, missing apps, etc. So, now I just wait it out.
I had to basically rebuild my iPhone 5s from scratch last week because I became impatient and cancelled the sync too early. It's taken me an entire week to move songs over (playlist by playlist). I sync a playlist folder, disconnect the iPhone, reset the iPhone (since I will often get stuck in the "Waiting for sync to start" phase if I don't reset), sync another playlist folder, etc., etc.
Entirely frustrating.
It's probably because I have a huge library, but, really, if they're going to release iPhones with 64 GB and now 128 GB storage capacity, they have to expect that some people have huge music libraries??
While syncing one playlist folder (that had a lot of songs on it), I literally left my iPhone in the syncing stage for over 12 hours. I left for work, came back, and it was done. Everything copied over fine, but, seriously??? 12 hours? That is ludicrous.