1) You will not have to purchase drivers etc. for the new drive. All you will need to do to set up as a slave drive, is to change the jumpers accordingly.
2) I can't see any compatibility issues with the drives.
3) Probably the new drive would be better as your primary drive, but if the original is working fine, why not leave things as they are?
I hope this helps
There will, of course, be others with different ideas.