Yes Rachel, of course Willoughby isn't drunk. HIs over hyped manner does lead Elinor to suspect it, but it is just a lead on for him to tell her that he has driven hell for leather, wtih just a 10 minute break out of his carriage to eat and drink something

As for Eliza not knowing W's address, I've always foudn that hard to beleive. Surely unless their relationship is all physical, he must have told her a bit abuot himself at first when htey met and as tehy met in Bath, where he was known, he would probalby tell her the truth? So surely the first thing you'd tend ot say woudl be that "Im Willoughby, I have a little estate in Somerset..." and that way,she coudl surely have foudn him or at least his home, easily?