To get yourself 90% towards nailing down Exp numbers, implement how experience is gained, play-test, and when you think to yourself, "the player should get a level about now," record how much experience is accumulated, and do it again for the next experience level until you have a number for every level.
In the end, experience charts are all judgment calls based around game flow (i.e., the judgment call behind Dungeons & Dragons 3rd-Edition exp numbers is "13&1/2 fights to get to the next level").