[Bicycle Bob]

I see a huge variety of roll bars - surely you can minimize that drag. I don't see windshields and side windows, but I don't see a rule against them. Even with the increase in frontal area, completing the cockpit with an attached vortex looks like a win to me, if done well.

One nice thing about small wheels is the reduced surface area friction, but I'd choose wheels based on available rubber. I'd also think about adding a belt to any tires I could find, and doubling the pressure. That makes suspension more desirable. You want to keep the roll center very close to ground level to avoid undue scrub. With narrow tires, camber control is less of an issue for traction, but any suspension can help or hinder cornering speeds, depending on how it is done. Solid axles are a good way to get started with suspension, but you MUST have a bend in your tie rod, giving it a bit of flex, or the Axle Tramp can wallop you.