Yeah the best chance for characters in the morning is at the hotel. I queued up last time with all the little kids, on my own- 22 years old at the time and my autograph book LOL!!
yes its Fantasyland and Discoveryland which are open for EMH (plus Main St and the Castle of course). The Main Street vehicles are often out and running up and down Main St during EMH.
Its only some rides too - generally Peter Pan, Teacups, Dumbo, Carousel and sometimes Snow White or Pinocchio in Fantasyland, and in Discoveryland its Buzz lazer blast, Orbitron, Star Tours and Space Mountain.
You get EMH if you stay in an on site hotel or if you have a Dream Annual Passport. This year, for the 20th anniversary, they allowed people having the Fantasy annual passport to enjoy the EMH, we are not sure if it will be this way forever.