I have a long layover at terminal 4, but am not sure if I will be able to check in my bags for my ongoing travel. Do I have to have checked in before I can go through security?

Yes

Depends if you're coming from an international flight. I usually land here from international flights and after customs I have to pick up my bags, go through security and check them back in. You need to have your boarding pass in order for you to go through security.

You require a boarding pass to get through security