unit sizes and gameplay

[seleucid empire]

ok this is a question for the more experienced players out there regarding, the small, medium, large and huge unit sizes. What are the effects of these sizes on:
(I only play on huge to make it more epic)

1. Blitzing? - I notice that in a lot of pictures people post up in which they have conquered the world, they use smaller unit sizes like 80 men per unit. Does it make a difference? Ive always beeen curious about this since every single picture ive seen with a successful world conquest is on 80 men unit sizes

2. Battle Casaulties - less or more? Are the battles faster? slower? easier to control? I notice that in battles screen shots, the players using smaller units suffer 1% casualties when facing a full stack compared to like 5-10% i see from battles using huge unit sizes. will phalanx based armies suffer because they cover less space making the phalanx more easy to flank?

3. Economy - Do the smaller units cost less to train/maintain? And also since your unit takes away less of the population because its smaller does it increase the number of taxpaying citizens in your cities compared to a game with large unit sizes therefore making you richer in a game with smaller unit sizes?"

4. Is movement speed the same for armies?

5. Will your game be faster? Are units routed more easily making the battles and the game quicker?