As far as screen protectors go... you've got plastic (ranging 10-20 each) or tempered glass (ranging 20-40).
I'll let you research which YOU prefer but I'll NEVER go back to plastic having used a tempered glass screen protector.
Seidio, Spigen and Mimi seem to be the top brands with different features (and advantages and disadvantages to each). Having owned a 2 spigen glas.tr and 1 seidio vitreo, I'm personally inclined to choose the vitreo (even though it is more expensive then the others).
As far as cases go, that's a personal decision also. Not all cases are created equally and a 5 dollar TPU case may protect just as well as a 100 dollar high-end case. At the end of the day spending at least a few bucks usually doesn't hurt to protect a device though. My advice on this is get one that provides a lip so if you have the phone face down it doesn't come in contact with the glass.
You have options like a basic TPU to Tech21 (think that's the name) to Spigen to UAG to Seidio Surface/Active, etc... Once again, preference.
I have a Seidio Surface and Spigen Neo Hybrid (like the feel of it but not the quality).
