Multiple Enemy Stats and Scripts

I am going to be having various enemies in my game, however currently I only have one. I am just looking on some advice on how best to organise my scripts.

Is there a way to have a generic script for all enemies that will contain common variables (stats such as health, defence etc.) but so that these stats can be different for each enemy? Or will I need to write a new script for each enemy with different variable values?

Also, at the moment I have a script that contains code for enemy movement, enemy receiving damage, and then enemy variables (stats). Is this bad practice? Should I split these scripts into their own?

Is there a way to have a generic
script for all enemies that will
contain common variables (stats such
as health, defence etc.) but so that
these stats can be different for each
enemy?

Yes, create a base class that has all the common variables/members and inherit it for your enemy implementations. That will cause the classes to have a common set of variables.

Or will I need to write a new script
for each enemy with different variable
values?

You do not if they have common variables/members, this is whats great about modern programming languages. The goal is to not repeat yourself and generally if you are, you should look at your implementation and class hierarchy in general.

Also, at the moment I have a script
that contains code for enemy movement,
enemy receiving damage, and then enemy
variables (stats). Is this bad
practice? Should I split these scripts
into their own?

Again, if the information is common, you can just create a class that has the common information so you write it once and can inherit it with other classes to share that functionality.