Ezpatari,
Headliner (or just material) can be had from Re-Originals though they take a while, which they said would be the case up front. Alfastop may carry it as well.
Regarding dash color, I think it depends on your choice of body color, your choice of interior color, the original color of the car and your long term plans for the car. There is a middle ground between these. If the car was originally red, and your paint scheme is going to have red in it, I'd use the original shade of red and paint the appropriate interior parts the original red. This way if in 10 years SS's are $150K and you decide to sell out, you can just paint the outside back to original and ask top-dollar.
Regarding paint schemes, I'd be tempted to let the above line of thinking inform my scheme choices. Use the original color as the basis for your 2 or 3 color scheme and paint sills and jambs and engine compartment this color so it's easy to go to stock if you decide to sell someday.
Regarding actual paint schemes, this picture has a kind of cool 2 tone going on.
Alfa Romeo Sprint Speciale