the setup is good especially because its all done for you..
if you opt to go for the celeron one... dont!
i assume you are getting it all from mp3car site?.. you will obviously need a powersupply for it (carnetix or simmilar)... put it under the seat if you can.. its more permanent, and you dont loose the glovebox... trunk is too far for your high speed USB devices like DVD burners....
You obviously want something small.. look around for MiniITX boards and get a decent processor, possibly dual core.. get whatever case you can find that fits the dimensions of where you want to put the thing...and for screen... if you want it readable during bright days... save up and get a transflective screen.... i am NOT looking forward to summer.. can hardly see my screen is on..