Future Prius C owner

Hi all, my first post here and I am glad to find this forum. It is so helpful and I learned so much about the prius family!

My wife is interested in buying a prius c but I do have several questions in my mind before I pull the trigger....

1. How's the soft-tex materials feel like in Trim 4 compare to car seats cover like Clazzio? We are debating to get Trim 3 or 4, it looks like the only thing we need from Trim 4 is the color of the car seat being the cool black one but I don't know if it worth another $1500
2. How's the navigation system? I heard it is pretty bad and would like to get an aftermarket one like Pioneer or Kenwood, but then I have to downgrade to Trim 2 and give up the option of sunroof which my wife really likes...
3. Is it possible to have dealer order a custom-made Prius c? Would the cost be substantially higher?
(This may sound dumb but if I can get a Trim 3 and trade the navigation for the sunroof option that would be the best....)
4. Does prius c have a back-up sensor? If not any recommendation of a good back-up sensor system? (I know the alternative option to back-up sensor is back-up camera and I read the thread about it....but I've only installed aftermarket in-dash GPS before and I still have no idea how to get the wire all the way to the hitch area.....so I thought back-up sensor is easier to install?)

Thanks all!