I assume you have never rooted before, right?
You do not have to flash custom ROMS to get the most out of your root, and it doesn't increase your chances of bricking your phone anymore than flashing a custom ROM does. As a matter of fact, rooting doesn't even allow you to do that. You have to unlock your boot loader in order to flash a ROM, and most ROMs you flash will be rooted out of the box. But that is another subject entirely.
The likelyhood of bricking your phone to the point that you cannot recover it is very low. As long as your phone will boot to recovery you can always go back and restore the phone to factory default. Are there exceptions? Sure. Just pay attention to all the steps for your specific model phone and you'll be fine.