LCD brightness: 250cd/m2 vs 400cd/m2

Yes, 60% - 250 cd/m2 is low and if viewed in a dimly lit (almost dark) room, it will be ok. I would go for the 400 cd/m2 which is the max brightness of an older laptop.

Regarding brightness, higher is not always better. However, you can always turn down the brightness to the desired level.