I'm a new honeybee keeper, but my mother has kept bees for a few years, and her father kept them during my entire childhood.
I would caution against buckwheat. Mom said Grandpa planted it one year and it ruined his crop. The bees will use it, and make honey, but it doesn't taste as good. Mom said it was really dark, and would be good for industrial use, like a generalized sweetener IN something else, but not so much for regular honey consumption.
I'm a little afraid of how my honey will turn out, since my mom's honey is beautiful pale gold, and it seems a lot of local honey in these parts is super dark(think apple butter), so I'm very interested in planting, transplanting & seeding for my bees. A big job, since they can travel 5 miles. My goal is to make their immediate area so lovely that they won't have to.