So here is another chapter in my continuing tour through various ways to play Civilization V. It was well known in the earliest patches of Civ 5 that building the maximum number of cities was the strongest approach, using maritime city-states to feed them. Patches have nerfed ICS to some extent, and maritime food to a large degree. There hasn't been a whole lot of material written on the post-patch Civ 5 world, though, so I'll give this a shot. (This was played before the June 2012 patch related to the Gods & Kings expansion.)
The chief limitation on ICS is the global happiness cap, so a good civilization for ICS gives something to work against that. Egypt would seem to be the best choice by a wide margin. +2 happy on an early unique building, which goes to +3 with an easily accessible social policy. And the wonder bonus is all good too.
My variant rule to force ICS gameplay is this: Every city must be founded at the minimum 4-tile distance from another city. No, that's not any kind of severe restriction, in fact it's probably what you do anyway in most games. But the point is to enforce going for maximum city count rather than slipping into picking better locations.
I also have very specific Social Policy plans going in. This isn't a variant rule, but the policies that must be targeted are Liberty full, Organized Religion in Piety (+1 happy from monuments and temples), and the Order opener. Even with the widest empire I can get, I think I can make 9 policies by the time the industrial age opens.
Game parameters: Large pangaea this time, wet with low sea level. Emperor difficulty. Note that cities only give 80% of usual anger on a Large map, meaning 2.4 per city.