Default [Q] Please help w/ getting back to stock.

I don't want this post to be too long but I need some help here, let me sum it up.

I purchased a secondhand Note3 off Ebay to replace my Note2. I got it an it appears to me that it's been "modified", I see this SafeStrap thing at startup and a SuperSU App. Once I saw this I decided to hold off on putting my sim card in and have just been using it on wifi. I used the "RootChecker" app to see if it's rooted and it tells me yes. System info tells me the phone is running 4.3. I know not much of this rooting, flashing, roms, kernel scene. So:

- My goal is to get this phone back to stock setting, no SafeStrap or root of any kind if it's there, so the phone operates and is just as it would be if purchased new from Verizon. What is the easiest way to go about doing this?

From there I might actually think of trying my hand at rooting this thing since it's a secondhand device, but I first want to eliminate any modifications made to the phone by the previous owner, and if I do root I want to start from ground zero and do it myself.

I apologize for my ignorance in this but could really use the help and hopefully learn more about this world along the way since it seems everyone who roots swears by it, I must be missing something but for now my objective is a clean slate with this device

Thanks in advance.