well I think it will be easy to get a few of the favor items early on, but i think it will take a while to get all of them, because while you can get some of the easier achievements quickly, it will take a while before you can complete some of the harder ones.
as for maps, i would guess we'll probably get some more of those, maybe even when they give us the new demigods.
I'm sure they will add or adjust items here and there, but mostly for balance. As for skills, I'm sure there will be balance adjustments over time, but I doubt that we will get new ones at release since right now they are balancing all the skills for release.