I suggest you guys check out the Hammer and Tongs website, since they're the ones producing it.
http://www.tongsville.com/Especially nice are their two regular shorts. The Pool Cleaner and Eiffel's Blessing. They might help give you a feel of these two guys. I found it strengthened my trust.
I've been reading page up and page down of interviews and the likes, and the writer, who admittedly hadn't read or heard or seen the original book, radio show or TV programme respectively, went into it with all his might when he got the job and has been doing rigorous research in the vaults of the Adams family. He's now read the book a million times over (or somewhere close to that) and likewise with the screenplay Douglas himself wrote before he passed on. He's also been using the unreleased little notes and things Douglas has been sketchin up over the years to make sure he stayed true to his final vision.
I, personally, think Marvin looks great. Sure, he looks like he'll be a neat looking toy as well, but I also think he looks supremely depressed. I hope you weren't expecting to see the Marvin you knew from the TV show? Also, he'll be played by Warwick Davis, whom most of you know as Willow Ufgood or most of the little people in Harry Potter. He's a very good actor, though I'm interested to see what'll be done with his voice.
A black Ford Prefect? Why not? It was never stated otherwise.
Finally... Sam Rockwell. I mean... Does it get any better? Anyone who's seen him in either Confessions of a Dangerous Mind or Charlie's Angels should vigorously nod their heads in agreement when I say that he'll be the perfect Zaphod.