Actually no it wouldn't be to much. After all the first 7 are free so. It would be a different story if you had too buy all of them, since it might get to expensive. So like 10 should be enough. Just remember to make them harder to achieve as you get higher, so it doesn't take like 3 days to get all of them. But the last 3 have creative mode too so that they would work even harder..And I would also say griefable in some places, but not all. like spawn and if u have like a plot world or something no. But if it is like a mine and a survival world then you should be able to grief.