In general it's easy. Although gone are the days of limited security to overcome and the ability to hide (for warranty purposes) the more serious custom activity. AFAIK rooting is still simple enough and fully reversible.
The things to be cautious with are odin and anything related to bootloader changes.
The things to be aware of are that flashing custom roms will very, very often require a full data wipe - so too do the troubleshooting guides if anything goes wrong.
I recommend you should make sure you have a good copy (md5 checked) fully stock rom matching your current one. And a working copy of odin installed and check you can connect to it properly (just don't flash anything!) This is often your "if all elses fails" tool.
Read twice, double check your files, and trust no one person unless they're recognised.
If you haven't read prepare to be ignored, or worse.