It's your ride. You need to make decisions for yourself.
I'd suggest perusing the Show Off Your Project forum for ideas. There's pics of lots of different rides with all sorts of setups. A breeding ground for ideas as well as e-coli (J/K-the coffee's starting to kick in).
Also, it helps to know what your options are. If you're determined to keep the stock stereo, you're looing at either a monitor hanging somewhere off the dash or center console or possibly a flip-down monitor on the ceiling.
The most important thing to remember is that it's convenient for you when driving, since a touchscreen is used for PC control. You don't want to be reaching over to the passenger side to skip over that Seals & Croft tune your girlfriend/wife/daughter/kitty-cat/gay lover loves so much.
Have you looked in the FAQ yet?
How about the Wiki?
Under normal circumstances, a signature would go here.