Here are some brief answers before Onyx comes on and gives you a wise essay
What is the standard points size of the game? Tournament size?
How much AP vs AT?
Many units have both AP and AT values, but the key thing to keep in mind is ALL units can attack vehicles (and act as AT) in assaults. That means you don't have to go out of your way to make sure you have an exact ratio of AP to AT to have a balanced army.
Is there any requisite of x% in Core/Special?
Each codex has its own requirements of Core to Support formations, and many also have a Navy and Titan allowance. It's usually something like '2 support formations per 1 core'.
Are transports as prevalent in Epic as they are in 40k?
Yes, they are cheap and Epic is a game of maneuvering for objectives (even more than 40k). There are plenty of foot and mixed armies though.
Is there any class that is an auto-include due to how powerful/important it is (ie Titans/Flyers/Super Heavies)?
Depends on the army, all want some sort of anti-air and the majority of Imperial Armies benefit from the inclusion of a Warhound Titan (fast, resilient, and everything scores).
Is the game relatively balanced army vs amy?
Yes. It's not perfect and there is a bit of variance between them, but it does seem like player-skill is more important. Someone like you could probably make a competitive army out of virtually any codex.