Look. You don't have to like 3e. A lot of people didn't, but you are making a mountain out of a molehill with this particular complaint. You need zero knowledge. Why? Because...
Player: "So I'm playing a Cancer Mage and now I have this disease(can't remember the name) that gives me...
Not really. One simple announcement in session 0 about disallowing broken uber combos like Pun-Pun and the Cancer Mage thing and they'll know that if they try it, it will fail. Then you don't have to go through anything. You just nix stuff that they try, if they're the kind of people who...
What. Just because my 20th level wizards could, even if totally surprised, cast Celerity or Greater Celerity as an immediate action to gain a standard action and possibly move, use Sudden Maximize on Time Stop, spend the first of my 5 rounds dazed in said Time Stop in order to not be affected in...
That's putting the cart before the horse. XP is earned as you adventure in order to advance you as you go along, not to get you ready to practice stuff. If all it is for is to show what you already learned in training, then it become entirely meta since it represents nothing about improvement...