Aftermarket Radio Install Questions

2002 Mazda Protege5
Hey everyone,

So I finally put money down on a pioneer aftermarket radio and replacements speakers. I've never done this kind of project before and I am not the most knowledgeable when it comes to wiring... (nervous)

I purchased the Mazda Protege5 wiring harness and used crimp butt connectors to connect these to the wires of the aftermarket stereo harness.

This is a dumb question.. but do the grounding wires in the photo below need to be connected together or do they both need to be connect to the chassis?

If the answer is "they need to be connected to the chassis" then does the metal in the image below I am pointing to suffice? What part should I use to secure the grounding wires to this?

Lastly, apparently there is a brake wire on the aftermarket stereo wire harness and the bluetooth and a plethora of other features on this radio wont work if this wire is not connected to the brake. Is this a pain in the butt to accomplish?

Is there anything else I should keep in mind while installing this?
2002 Mazda protege5
Also the only thing that wouldn't work is video playback. The wire gets grounded when you engage the E-break. Just a safety feature so you can't watch while driving. It can be grounded constantly which tricks the unit into thinking you're parked
2002 Proteg5 manual
My parking brake wire actually runs down the center console to the actual wire for the park brake switch,