Good material combo?

That's a very sharp combo- reminds me a bit of the b/w cobblestone with black vinyl I see on some 150 '57 Chevys.
If The addition of a gray beading if possible - that would look great as well.

It is really hard to choose a black vinyl without seeing it in person. There are dozens of black automotive vinyls, and the Madrid grain is one of them. Stop at an upholstery shop and ask to see their black vinyl swatches. The houndstooth will look great with any of them, but you might find a grain pattern you like better.

Does the material change what thread you use?

I was just wondering do you use the same thread on all seat materials or does the material you choose have an impact on your thread?

The only time I use different thread is for decorative purposes. I may use a different color or larger size to make the thread stand out more, but as far as just sewing the pieces together, I use size 92 polyester for everything.