[thejeff]

1) There's no limit on army size. There are limits on the total number of units. They are high, but reachable in big games - particularly with Late Age Ermor and R'lyeh since they spawn many free weak troops.

2) No turn limit.

3) Easily months, for large MP games. Late game turns can take hours.

4) Decent at early game. It'll will give you a challenge for awhile, especially on the harder settings. Has trouble countering a lot of specialized strategies, as more options open up in the later game. I tend to play smaller SP games to minimize the AI's weaknesses and to minimize the late-game micromanagement.