They're not terrible offroad, but I would certainly opt for a Hijet or Carry if I were in the market for a hard-hitting offroad-oriented kei truck. Those trucks have solid axles with leaf springs, a mid-mounted engine, and lift kits are readily available.
The Sambar is a good road-going truck... more comfortable ride, quieter (rear-mounted engine), higher top speed, and smoother than the others. Honda's model, the Acty, is similar with its rear-engine/independent suspension setup, but it's full time AWD.
Nope. All 90+ kei-class trucks are powered by a gasoline 660cc. Earlier models are 550cc.
Nope, they're actually quite different. I suppose the STi is just a badge-engineered Evolution since they both have four doors, a trunk, AWD, and a turbocharged four cylinder, eh?
Colin