1. I had a CVT Mk 3 Jazz in 2015-16 and averaged 57.8 mpg (fuel into tank) over 5300 miles.
Mine is 46,3mpg, manual, 35500miles.
3. I would hope that Honda would use a battery pack larger than 1 kWh in the Mk 4 Jazz. Otherwise the little battery will have a hard life and the hybrid system will struggle to give much benefit in other than simple stop-start-accelerate-brake urban driving conditions.
CR-V and Accord have a 1,3kwh lithium ion battery pack, the Insight has a 1,2 kwh, Jazz Hybrid hardly will have a bigger pack. Toyota HSDs have similar capacities (Yaris 0,9kwh); using the electric part only for efficiency purpose, a bigger pack would be unuseful.
Just to pop back in (hi to those who remember me) my Corolla (1.8 Hybrid) has averaged some 10% better than my Jazz after nearly a year. My Jazz used to manage between 49 (winter) and 54 (summer) mpg over the year, excluding long journeys. My Corolla has managed between 55 and 63. Same driver, same driving style. Bigger wheels. But its worst figure in the depths of a cold wet winter was better than the best average my Jazz could do.
Even long journeys are surprisingly better, albeit not by much. I typically get around 65 to 70 on the 180 mile drive to my Dad in the Corolla. The Jazz was between 60 and 65.
Oh and its e-CVT gear box is as efficient as a manual because it's all done with gears.
But that isn't the best my car could do. On the Toyota forum I now frequent there are a couple of taxi drivers and they've been averaging 70 to 80 mpg.
It'll be very interesting to see how the new hybrid Jazz performs because comparing the CRV and the Rav-4, the latter has more power and is more efficient so the evidence so far is that Honda's hybrid system is just not as good as Toyota's.