First, wondering if putting some brakes, other than Honda brand brakes, is ok, such as Raybestos rotors and pads.

Also, will putting 17's and two 12" speakers add too much weight to my stock 126 hp 2000 Honda Civic EX?
Thanks.

aftermarket brakes will be fine.

17s and 12s on your ex will be fine.

As was said, aftermarket brakes are fine, and 17's and 12" subs will be fine also. As for brakes, powerslot rotors and Axxis/PBR metal master pads are a good combo for street use if you are looking to upgrade the brakes some.

yeah, powerslot is good brand. if your into AEM the've teamed up with powerslot and have made AEM's rotor kits a lot more quality than they were before, but the brake pads are still handled by AEM.