First of all, welcome to the DIS!
Are 4 character meals too many for a 2 year-old? Obviously, the answer depends on your son, not on me. I don't think 4 is too many -- I don't think 10 is too many. But I think you have to evaluate that question in terms of a) what your son will enjoy and remember from his Disney trip (and that's a LOT more than you think!), and what you're doing for the rest of the time.
Based on our experiences with DD5-going-on-25 when she was almost 3 and on her first trip, I'd say there are two factors to consider.
One is your son's comfort level with characters to begin with. How scary is Goofy now, really? The answer? To a two year-old, Goofy can be damn scary! He scared the pants off DD at Chef Mickey's, which was our first-ever character meal. Fortunately, we had to wait for a table (Goofy was at the entrance), and she calmed down.
Even more fortunately, the first characters to come to our table were Chip & Dale and they stole her heart. By the end of the meal, she was dancing in the aisles with Minnie, and had a wonderful time...but it was a stressful start.
I'd remember that human characters (especially beautiful princesses) are less threatening than character-characters, and that Chip is a lot less threatening than Shreck for a little person. The little guy is going to enjoy Pooh and Piglet much more than Haunted Mansion.
The other factor has to do with the basic physiology and psychology of two year-olds. They are built closer to the ground than we are, they therefore see many things we don't see, and objects are a LOT bigger to them than they are to us.
WDW is a LOT of stims for a little kid. When we walking down Main Street, we're wondering where the bathrooms are. They are being bombarded with an endless stream of stimuli -- sounds, smells, colors, movement, people, characters, balloons, photographers, horses, people bumping their stroller, looking around and not seeing Daddy or Mommy, etc, etc, etc. That endless battering wears them out, as you will find if you experience the "Monorail Meltdown" at the end of a long day. Most of us have been there, and it's not a happy place.
That overwhelming pool of stimuli is the environment that character meals -- and rides, and meals, and trips to the bathroom, and standing in line, and being lost, and being hungry -- occur in.
Is four character meals too much? No; I don't think so. Can you wear the kid out and ensure that they have the worst time of their lives without ANY character meals? Oh YEAH!
The key, IMHO, is not how many things you do, but how you accommodate the little person's needs. Start early, take a long break in the middle of the day for pool and/or naps, and you'll be fine. Drive the little weakling from dawn to midnight because you're determined to earn your WDW Commando medal? You'll pay. Oh, how you'll pay!
We ate at Kona Cafe and she kept saying, "Where Pooh? Where Mickey?"
