Well, I guess most of this you'll find out with some playtesting of your own (major problems with the mod really don't show their face until about turn 60 so you really gotta do a full playtest). Putting science into military is not very good, as the extra happiness hits promotes more lower military. So beelining Civil Service is the only way to go after some little ancient era techs.
The reason early-mid game ICS doesn't let you compete on immortal/deity is that you're outexpanded by turn 80 (you could get it by 60 with some very early investment in scientists, but it slows your expansion too much). You can't ICS very fast without the farming food policy or civil service. I'm not sure the exact mechanic causes it, but even on immortal the enemy builds pretty rediculous hordes. You can take cities with a rush, but there isn't much point until civil service.
As far as difficulties, you want the range to be larger than king-immortal because it gives players less of a jump in difficulties. If king is too easy and emperor is too hard, people will just stop playing. I'd actually recommend my "extra difficulties" mod component, as having "halfway" difficulties would benefit this a lot. It's just an xml file or two so merging would be no problem.
Lastly, you don't want such a huge focus on food because it limits strategies. Expanding strategies is really the entire reason for eliminating ICS. If the only way to play well is to spam farms everywhere and always take food policy, it gets pretty tedious.
