I dont think there is a 'minimum' dose.. Depending on smoking method, 10-20mg should def make you feel something.. Personally I dont really like low doses of DMT, (unless if its the pre-launch dose to get a bit accustomed to effects again, followed by bigger dose), I feel that low doses = the 'weird' initial physical effects, but not all the amazing stuff that happens with higher doses. But I understand if its your first time and you want to test the waters.
You say sprinkle on bud.. How, joint? If so, I dont recommend, very innefective. Maybe better in a bong, but be sure to put a thin layer of herb (or ashes) on top too, and go easy on the lighter. Good luck!