The single biggest thing I look for in my bikes is ease of maintenance, this extends to parts cost in my book. This is followed closely by bike weight. Honestly engine displacement is hardly even on my list of needs, any of the modern 250cc engines will take you down the highway when needed. Other things I think of is crash protection and fuel capacity. It used to annoy me that my KLX only has a 2 gallon tank, but I just carry extra fuel when needed and have come to like the lighter weight and thinner dimensions of a small tanked bike. In your design a set of removable axillary tanks would be brilliant if you decide to spec out a smaller tank. Small fixed tank for hardcore off road, then fit the "drop tanks" for long trips. Anyway As far as my details I have been riding for 4 years, and I do not own a car, so I ride rain sun or snow, and I average about 15K miles a year. I usually ride about 70% on road and 30% off.
I do stupid stuff, brace yourself...