So do we know how far the 2nd season is supposed to cover up to?
We don't know for sure, just that the Berserker Armor will make an appearance. Assuming of course, the show doesn't get cancelled halfway through due to poor ratings as viewers burned from last season decide not to tune in. Keeps fingers crossed.
If I were to make a guess as to where the endpoint would be, then I'd say it would be when Guts and company flee Flora's home about a third of the way through v27. The first season roughly covered five volumes of material (17-21) plus about the last third of v16. Since that endpoint means they would have to cover about the same amount of material give or take (volumes 22-26, plus the first third of v27), I'd say it's a good estimate. But don't quote me on this.