So once we have a custom map ready and we want to test things out and balance the different start locations, are there any useful cheats available to see what the AI is doing? Specifically something that can give full visibility to the entire map during a game.

Huge +1 to this question. My current playtesting process has been to rush through the game on blitz/fast in order to see how certain parts of a map play out and look. This is especially a pain when I want to test out some high-traffic battle spots but I have to lure the AI into cooperating, haha. Additionally certain aspects of play operate differently depending on the game speed, so doing a normal or slow game may yield some different interpretations of areas on a map that could use improvement.

All to say, the process of iterating on a map is slow, especially when aiming to make maps that are competitive and reasonably balanced.