If it makes you feel any better you're not the only one to make mistake #1 & 2.
Marverni, Hinnom, and Tir Na Nog also made the mistake of attacking Agartha.
I don't agree with your third self-critique since 10-12 provinces per is not too cramped, although it appears that you had a slower expansion than Fomoria should have which led to a cramped position. Also, your strategy should have been viable since it looks fairly powerful early, mid and late game. I think you ran into problems because of your slow start and picking a fight with a nation that expanded quickly and had more resources early on.
Re: Happy New Year, New Game, New Players (noob EA game: Running))
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