My son has been twice now, at 19 mos and 28 mos. I think the best thing to do before leaving for your trip is doing some homework. Get your kid familiar with many of the characters and that will make it a bit better. My son has always been a big Mickey fan, he used to say night-night to him each night when we passed thru the kitchen with many Mickeys in it, so he was very familiar with Mickey and he knows that mommy loves Mickey.
His first day there at 19 mos, we went to Liberty Tree Tavern. He was a little scared of Pluto, Chip and Dale, but when Minnie came around he just lit up like a lightning bug! He was all smiles and flirts with her. He was not very familiar with the others, so he didn't like it as much, but he was very familiar with Mickey and Minnie is practically the same thing. The next day and the rest of the trip he loved seeing the characters that he knew, and he wasn't that familiar with others besides Mickey at that time. Others that he didn't know, like Rafiki, he hesitated a bit with.
On the next trip at 28 mos, he was a lot more familiar with many more characters and loved seeing the ones he loved. Goofy still scares him a bit, I think because he's just soooo huge. And he would be in the foulest of moods and cry when other characters would come by and he wanted nothing to do with them, but then Mickey came over and he was happy and smiling and cheerful and his mood was changed for the rest of the day. This magical Mickey transformation happened a couple times on that trip.
Definately don't push your child to hug and kiss them. Encourage and offer but don't push. A lot will depend on your child's temperament as well. If they are more shy they might not like it as much. But use yourself as an example, if they don't want to go up, you can go up and let them see how fun it is! Maybe the next time they will join you.