Yeah, unless the AI is playing a naturally amphibious nation it does tend to suck at getting into the water. It basically has to luck into amphibious indies. So bearing that in mind, I have a suggestion (which will also make the game a little harder). Make a random map that is either tall and thin, or a map that is very wide and fairly short. Put the noobs in the middle with AI nations on both sides. You will more or less get the funneling effect since each player will only have to defend a certain number of provinces, and you can do this without needing someone to make a map for you. If you are set on having the map come out to your specification however, I think in all probability you'll have to make it yourself. So if you have any games with a map editor you think might be able to do what you want....
I would aim for making this game as hard as possible. Pre-set gods for each AI with sensible builds would help, as well as setting them to impossible. I believe that is doable with mapping commands, though you'd have to ask someone more knowledgeable about mapping than me. Set the AIs aggressive, low indies... I would not recommend putting the resource multipliers too high though, actually I would stick to normal.
The only problem with giving the AI "powerhouse nations" is that it actually tends to do pretty poorly with them. If you want to give the AI strong bless nations, I recall someone having made an auto divine bless mod that would be a good idea to use. And, probably the nation that the AI is best with is LA Ermor
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