I was at Paris-Est just last weekend (picking up tickets from the Virgin Megastore there - very much recommended if you fancy going to the Louvre or Musée d'Orsay and want to skip the queue), and the famous "Association des Sourds-Muets" (the - neither deaf nor mute - beggars normally operating on RER B) were on the rue d'Alsace steps, grabbing luggage and "helping" people up with it. Shake your head and walk on.
I noticed that the bar at the top of the steps (the "au Train de Vie") has now been refurbished with all the seating now consisting of old train seats. Still manages to look rather seedy, though, but made me chuckle.
If you do want to get the bus, the easiest is to use the main front exit from the 'grandes lignes' station, to the left of the ticket desks, on to the rue de Dunkerque. The bus stop is in an island in the middle of the road, just to the left of the giant Terminus Nord brasserie. There's only one bus from here, though (the 26 towards Nation) but it does run every 5 minutes during the day. To be honest, if you're walking to one of the further stops from this, you're halfway there already. The buses take normal 't+' tickets, so if you get a carnet on the Eurostar, you can just dunk them in the machine as you board.