A 350w motor @ 36v will (just) meet your needs for the weight you'll be moving (level ground).
The 250w motor @ 24v on
my mom's electric bike has propelled 220 lbs plus a 65 lb bike at 20 km/h (12 mph) on level ground.
If you get a 500w motor where a 350w would suffice, you'll use it. So your range will be less
![Smile](https://www.fuelly.com/forums/images/smilies/smile.gif)
But you'll probably have more fun.
As for pack size, 9ah @ 36v is comparable to my mom's in total energy: The pack is 2 * 12v @ 12AH, or a 24v 12AH pack of 288 watt hours total capacity. It'll go about 20 km/12 mi on electric only. For comparison, 36v * 9ah = 324 watt hours.