If you look above you will see one company advertising a 35 mph top speed which is not legal anywhere in the US that I know of. The safest way to market to other areas would be to not make any claims over what the federal regs are for motorized bicycles and that potential buyers should check with their local laws and are responsible to do so. You can even provide a link on your site that will allow them to do so like this one here: http://moped2.org/mlaws.htm
Note that in the federal regs and in many states they state that there be an automatic transmission, as in this taken from the Nebraska site: "A moped is defined as a bicycle with fully operative pedals for propulsion by human power, an automatic transmission and a motor not exceeding 50 cc that produces no more than two brake horsepower at a maximum design speed of no more than 30 miles per hour." While this is generally not observed it is a written law and can be enforced potentially making you liable as your system is not automatic.
While I see that you have a freewheeling crank it doesn't look like there is any freewheel on the motor drive which would release parasitic drag when pedaling the bike with the motor disengaged. While not everyone wants to pedal there are those that do and the ability to do so freely is a good thing.
Also you may want to take down your phone number from your header as there are nasty bots out there looking for them and can cause you problems. If someone wants to get to you they will do so through your website.
I really get a lot of looks from people when they hear my bike changing gears as I'm riding along. I even had a few ideas on how your setup could be used on a tandem bike. As for the legal issues I'd print out what each state says you can operate on the public roadways. Then you can let the out of state customers know anything outside of that is for off road purposes only. Many places you deal with over phone let you know the call is being recorded. You might consider doing this as well.
Hey, everyone this is the first message of hopfully many threads. I have read some things on this forum about people in our area looking for builders of motorized bicycles. anyone interested in this look at our website autoservus.net