Good topic. I just ended a game on large map and think that is an advantage for my play-style. So I'm going to do medium and smaller maps, NO dense monsters (as my Sov gets to much Xp), NO frequent resources nor magic shards (perhaps even the lowest settings). This will make the game more challenging for me.
And no more than one hero per army isn't a limitation in my play-style. I always do that as it gives better Xp to troops. Always 2+ heroes in an army would be a limitation in my eyes.
Regarding the Pioneer-exploit: By queuing up many Pioneers (after the thing you want to build) the city's growth-rate can increase. You can get a maximum of +3 growth from a high food surplus, but this is calculated on the current population of the city. Each Pioner in the queue will decrease the population by 30 (to cover the unit) and change the calculation of the food surplus. It doesn't work on newly founded cities, but when they get bigger and starts to slow down due to lack of food, then you can increase the growth rate using pioneer-queueing. The city cannot grow over its maximum anyhow - so you often still need to produce food-buildings to reach next city-lvl.