i actually prefer to stay agriculture over GoN with calabim as leaves, so you can get population faster (GoN may raise the happycap, but the population comes slower when you do reach it, and agriculture with the ancient forest extra food means you can grow fairly big even with unhappiness, then you just eat the unhappy people)
lots of xp seems good, but you start running out of good promotions after 82xp i find, so it tends not to be too great for heroes (they need to be level 6 just to get vampirism, so all you're really doing is fast tracking them from 26xp to 82xp, which they wouldve gotten anyways, and then after that its filler).
where vampirism really shines is in casters, since they gain xp automatically, so you can farm out a bunch to get them to level 6, then get them all the promotions they need for spells once they're vampires.
but about your other points, archer of leaves aren't worth it, too expensive, and you can do much better by rushing for hunters with a normal civ and then rushing your enemies with them. taking the long route to calabim hunters (which also have -50% city strength on attacking and defending) won't win you the game unless you wouldve won without them.