Yes, the charge wire should be on a ring terminal on the back. You should be fine stacking a second one on top of it for the larger wire.

As for adding accessories, you will go to the battery, but not directly. You need (should) use a fuse or some sort of overload protection between your accessory and the battery, and it should be as close to the battery as possible to eliminate a lengthy run of a hot wire before the fuse. This is also a chance to use a power distribution block if you have several items to add. There are endless ways to do the wiring, just pick what works for what you need.

Michael