I'll try to hit a few of these from memory...
Seat height - It's the same as the Enertia. There is a change to the ergos, though, as the handlebar is about 1" further back towards the rider and just slightly higher. This new position has been preferred in side-by-side comparison and riding tests for tall and short riders.
Brake position - No chance of a left hand master cylinder. We're going to stick with motorcycle standard controls as described by the FMVSS (Federal Motor Vehicle Safety Standards) unless we start building a scooter.
O-ring Chain - You have spoken and we have listened. O-ring chain will be standard on Enertia Plus.
Radiator vs. Fan - A water cooling system simply adds too much cost to the bike, unfortunately. The motor is more expensive with the added water jacketing, a custom aluminum radiator is expensive, a small, reliable 12V water pump is expensive, and the added bracketry and assembly cost all add up as well.
Top Speed - stay tuned...
FYI... hardly anyone's noticed that we've bumped the battery bus voltage up to 88.8V nominal vs. the Enertia's 76.8V.
Keep the input coming. Very helpful!