wow ... that is the nicest bmw i've seen ... absolutely beautiful.
Regarding sound cards ... Depeinding on what mobo you use, I would suggest using a PCI card as opposed to an external USB card. A lot of people have problems with USB soundcards and windows for various reasons ... The main advantage to USB cards is in a compact design you can place it anywhere in the car. But like I said, sounds like You'll need a full sized PC here, so if you've got the room put in a PCI. You can always run cables if you want to mount plugs on the dash.
If you're that big of a SQ nut, maybe even look into professional sound mixing cards.
If the money's there get xenarc LCDs ... If not go Lilly. I like my lilly, but you seem to be more of a perfectionist than most on this board, and I'm sure the screen failing on you is not an option. and definately go touchscreen.
as for video ... again if you're going with a full size pc, check out matrox. They have a number of multimonitor cards. JUst browsing I came across the QID:
http://www.matrox.com/mga/archive_st...ox_qid_pro.cfm
Looks like it'd do what you want and then some ... i'm sure it's expensive.
For Power ... invest in a GOOD DC-DC power supply ... Check out OPUS, or maybe a Sproggy from Mastero ... there area also other supplies available on the net. Again ... if money's no option, get something expsnsive.
hth ... good luck and for the love of god keep us posted!