My mother and father's funerals, I can relate on some level to some of the feelings you are wrestling with. You love your dad. He loves and, more importantly, he respects you. He wants YOU to speak. He knows you. He knows you will be emotional. He is good with that. He also knows that you will pull it together and say things about him to those in attendance that others can't or won't say. You are now his mouthpiece to his posterity and to his surviving friends. God bless you and your family.