Over the years I see many pilots out there flying as low as possible, just because they can. Which is probably one of the worst reasons for doing so. I would strongly recommend that you fly enroute at least 200 AGL. The reason is that below 200 AGL obstructions are not required to be marked, painted or lite. Way too many wire strike accidents happen enroute with pilots flying low just because they can.
As for going higher, keep in mind that unlike many airplanes your maximum speed decreases due to altitude. So unless there is a significant increase in ground speed there is no major benefit to higher altitudes.
Enjoy your trip.