if I know nothing about Android, is it crazy to have a rooted phone? I bought my first Android phone off ebay, a Samsung Galaxy S4 after always using Windows phones.  It was supposed to be unlocked and a "store demo", but when I started playing with it, I was getting warnings that it was rooted and couldn't update in the regular way, etc.

I tried to update using Samsung Kies, which gave me a ton of errors, I had to do it four times.  This was the error message I kept getting:

http://i136.photobucket.com/albums/q161/Arylkin/1%20error.jpg

Then I got an error that I needed to do "emergency firmware recovery":

http://i136.photobucket.com/albums/q161/Arylkin/error%202.jpg

I finally got it to work (I don't know what kind of update it was, because it's still running the same Android version after it).  I got it to work by just ignoring the emergency recovery message and hitting continue (or something).

I am apprehensive about keeping this phone, since while I really do like it, I am worried about having some fiasco and it refusing to update down the road.  Also, every tutorial about rooting and "flashing roms" (whatever that means) and doing anything to a rooted phone says, "WARNING- YOU MIGHT JUST BRICK YOUR PHONE!".  Needless to say, this worries me.

The seller is willing to take it back, but now I've already bought a otterbox case for the S4 as well as additional batteries, so I'm kind of roped in to having an S4.

What would you do, return it and try to find another person selling an S4 that is stock?  I really don't know anything about Android, and even after reading tutorials, I'm not really comfortable doing a bunch of stuff to the command line of my phone or whatever, particularly since there are 1,000 warnings that doing so might totally break it.

Even video tutorials on rerooting or whatever have a bunch of comments like, "Now my phone is broken!  Thanks a lot!"  Everything I read says how rooting is the coolest ever, but I really don't want to break it since I will not be able to replace this, financially.

I'd appreciate any words of wisdom!
If it's rooted, leave it be. It's very unlikely for the S4 to receive many (if any) more Android OS updates officially since it's now a couple of generations old. I use a rooted S4 myself, and love the fact that I can remove bloatware at will and make backups of everything. 

With that being said, some more info from your device might help us direct you to info on your particular ROM if you have one, and how to lock it back down if you still so desire. Go into Settings>About Phone and see what Android version you're running and the build number for starters. All of those scary warnings in forums are there for a reason: with root you have unrestrained access to the very innards of your phone. If you start changing things in certain areas you can mess things up. However, it generally takes more than doing everyday tasks to do it. 

Armed with the information from the About Phone section, head over to the XDA Forums to find out just about anything you'd ever want to know about that phone, along with some generally very knowledgeable and helpful people.