Take a look at the usage spreadsheet in ppc750's signature:
http://brammoforum.com/index.php?topic=221.msg921#msg921Speed and hills are the two big factors in EV energy consumption.
I believe top speed on level ground is limited by a combination of maximum motor RPM and power output that rapidly tails off very close to maximum RPM. Top speed is 60 mph or a bit over. Weight and rider profile (tuck) are unlikely to make a large difference in top speed.
I've never sat on an Enertia, I like to stop and stretch every hour or so while riding on my gas bike, which has an upright seating position similar to the Enertia.
Riding an Enertia Plus at 55 mph will probably give a safe range around 50 miles, or 25 miles out and back -- so you're unlikely to be sitting for long enough to get uncomfortable. Riding at 35 mph might give 70 miles of range, at which point you likely would want to stop midway and stretch.
The Enertia isn't much more or less visible than other bikes. You can wear gear with high-contrast or reflective elements. The best defense is actively paying attention to traffic around you and avoiding (where possible) dangerous traffic conditions.
I don't believe the exhaust noise signature on my gas bike (which is fairly quiet) has any safety benefit save at parking lot speeds. In particular, the most dangerous encounter for a bike is an oncoming car or car at a side street failing to notice the bike while crossing the bike's path of travel. In either case a driver inattentive enough to do so is unlikely to hear the exhaust which is directed away from them.
The Enertia display has a state of charge (percentage) indicator, but does not display miles remaining. The Enertia Plus display may be different.
