I'm currently in the market for a car phone holder and I think I may have found the one I'm looking for in the imagnet. But before pulling the trigger, I thought I'd ask around and see what else is out there.
I bought an imagnet mount a few weeks ago and it's worked great for me so far. I think it's more convenient than a clip system type.
See here..... http://www.imagnetmount.com/
The Zenfone 5 is a really good phone for the budget. One thing to keep in mind is the screen. Drop it once and it breaks. It's that sensitive. Replacements are hard to come by too.
It doesn't need the amp and you don't need the case but if you really had to choose between them, I would say, take the amp. The headphones come with a bag anyways.