I like the stock rom, so can't comment on other rom's.

I've never had a virus, etc infect my Androids, and I've been using them for years. I am using AV on my S4, but only because it's easy and free, so why not?

Rooting is similar to jail breaking, as I understand it. It allows you to tweak thing at a system, called root, level. So anything from tweaking little stuff (like making the phone NOT wake up when the home button is pushed) to installing ROM's.

 

CyanogenMod | Android Community Operating System is a safe site. They do good work and their ROMs are a base for many other versions out there.

Anti-virus is an issue with many views on Android. Many, like myself, have run multiple devices for a long time without. Choose your download locations carefully. Never install any app you aren't sure of where it came from.

Rooting gives you administrator access to the entire file system, which in turn allows you to do many things on your device. It also allows you to muck it up royally if you don't know what you're doing. Read, read, read... ask many questions, then read some more. It's not rocket science and can add lots of cool stuff to your droid life.

 

Hi clip12, and welcome to the forum.
Let us know who your carrier is and we'll move your post to the root forum for that carrier, where you can get device specific advice.
Note that due to the phone differences across carriers, what works for a Verizon phone may not work for a T-Mobile phone (for example). Make sure you're reading about YOUR phone, especially when doing rooting research.
This would be a good place to start to help you understand. http://androidforums.com/samsung-galaxy-s4/760098-18-galaxy-s4-models-know-yours.html
As was mentioned earlier, rooting your phone gives you access to some really cool stuff, and some awesome 'powers' - but also enables your to really mess up your phone if you don't fully understand what you're doing. So yes, read, read, read BEFORE you root your phone, so that you fully understand how to root - and make sure you're reading about YOUR device, 'S4' is almost a generic term these days, and does not really indicate a specific device.

Good luck, and happy rooting.

 

Welcome to AF, clip12.
As stated above by Podivin, once we know your service provider and exactly which S4 you have, we will be able to put your questions about rooting your phone where the right people can see them and help you to successfully root.
If you choose not to root, that is fine too, but whichever way you choose to go, I hope you will enjoy your S4 as much as I am enjoying mine. It is a really nice phone!