I'm aware of that. But what would it take to survive the early game at all? I was afraid I had made this game too easy, but even these props wouldn't have sufficed on pangaea? A full Pikeman Army?
Do you allow for the luxury/resource exploit? Because if you use that, then you just need to keep the AIs happy enough so that they won't attack you and get some of their gold, perhaps so that you can keep them happy. If they're at least aggressive, I don't think that's generally difficult, because on an archipelago map they often won't attack you early even if you don't gift them some gold/tech every often to keep them happy. Then again, this is a CoTM thread, so I probably shouldn't assume that... except templar_x referenced it implicitly.
Lanzelot's strategy of gifting cities can work on a more land full map, including gifting the same city multiple times if desired (every turn in that thread involved gifting the city to an AI). I'm not entirely clear as to what you question is, but I would guess that the answer is a pikeman army with 7 hitpoints. They will attack a 6 hitpoint 3 defense army on flatland, but not a 7 hitpoint army. Possibly fewer hitpoints if you build a fortress/barricade in the right spot. Perhaps the AI won't attack a 12 hitpoint spear-man army in a barricade until they have tanks? I haven't tested that, but it might prove interesting.
Of course though, you'll probably also want a nice stack of artillery type units and some good offensive units.