Okay... well, maybe the suspension requirement was somewhat vague. heh.
I guess I am biased towards independent suspension. From what I've experienced in the "normal" car world, independent suspension handles better on not-so-perfect road conditions, but then again, it may be different for a superlight though.
As for the engine, I ride a BMW K1200 daily for commuting, so 5-6krpm cruising on the freeway isn't too much of a concern for me. Of course, if I'm building the kit myself, I'd rather work with a lighter drivetrain. The car will be used a lot on normal roads as well as as many track days as my wallet can afford, which means maybe 2-3 a year. If I had a choice, I'd prefer a higher power to weight ratio, and tq can come in the form of a supercharger or a very small turbo. :-)