If the Das Keyboard has Cherries, yes, they will fit on the switches.
Considering they look pretty standard, I would say yes, they will all fit.
To take off the keys with stabs, you can just pull at them, or lift them, and use something sharp to take the stabs off.
And they keys are ABS, but good quality ABS. They have a really nice feel and dont seem to shine too fast (got some shining on some, but then I use my keyboard a lot.