"IF" you want to go with the black interior you're going to need some parts because you can't just paint everything black.
A good friend of mine just changed his red interior to black and this is what he did. And his car not only got converted to black but also got converted from an AOD to a T5 along the way.
Black Vinyl Seat fabric from LMR (fabric made by Distinctive Industries) <<<< double thumbs up to the fabric!!
ACC Mass Back carpet
Black Dash pad bought from LMR
Black sunvisors from LMR
ABS plastic backed headliner from LMR
Black seat belt kit from LMR
Black A/C vents bought off internet used
Black rear carpet from LMR
Black door panels from AM
Door panel moisture barrier plastics from LMR
Black "Mustang" door sill plates
For the all the plastic pieces that could be removed from the car, I used a kiddie pool and soaked them in hot water (as hot as my spigot would get) with a heavy dose of basic concentrated Dawn detergent. I scrubbed them in the pool (forgot to take photo of the pool with parts in it!!) with a dishwashing sponge. After rinsing, I wiped the parts down with Eastwood's Pre. Then I put the parts in the pool AGAIN to do a final wash. The key is to get any of the years of Armorall and the like off the plastic.
For the dash (only part that did not come out) I wiped it with the Pre about 5-6 times and did a final clean with Sprayway glass cleaner.
For all the plastic pieces, I used two coats of Dupli-color adhesion promoter followed be 4-5 light coats of Dupli-color Trim Paint
For the dash itself, I used Krylon's Satin Fusion paint.
The key is light coats so you don't get runs. If you get runs use paint stripper and start over. And if you are curious, you can still see the texture of the plastic. You'd have too put on a crazy amount of paint to wipe out the textured appearance. In fact, Ford actually painted their parts in the factory to get the different colors. I could easily tell some of my stock interior pieces were gray and had been painted by Ford.