9 As far as logging into KDE. In your login screen is a button labeled "Session". Click on that and you can select "KDE". Login as normal and you'll have the KDE desktop.
What did you download for Clam? Post the filename of what you've got.
I wouldn't worry too much about getting the anti-virus software set-up. Now that you're running Linux you don't have to worry your own machine becoming infected. You can, however, pass one on to your Windows friends. It can't hurt anything to have it running, but I don't think it's vital.
Good luck on your journey. You've started the right way, by joining LQ. The forum contains the answer to just about any question you're likely to have. Beyond that, there are loads of people here every day that know Linux extremely well - most very willing to help.
If you have a 'go to' answer, please say where I'll find the 'go to'.
Good attitude. Very often we'll point you to the answer instead of just answering your question. This is not
meant to be rude. It's just to teach you the search skills you'll need to start to help yourself.