Those tracks are quite short, 30-40 seconds.
There is not so many offroad-sections, but the parts where it goes over grass are quite 'interessting' I think.
I made the track as wide as possible, the quickest line around turns is much tighter than the barriers.
Cars: I think UF1 and XRG are most fun, the UF actually feels fast on this.
(The setups are just as starting point, probally not very good ones.)