Sorry, It's just not going to taste like beer without malted barley, but the buckwheat might be interesting. Toasting any grain will cause toased flavors associated with a dunkel or the like, so you should be accurate there. Buckwheat has some sugars (3g/1cup flour), but how are you going to convert them? What was the gravity of the blonde with only 1 cup of 100% fermentable dextrose?
Every little thing is gonna be alright.