installing second amp

Im going to install 2 Kenwood 6X9s to a Memphis 250W amp in the rear of my car (all i ahve up front is 3.5", so no point in amping them). I have a few questions about the installation. 1. Should i run a new RCA cable to the other port on my hu, or should i daisy chain it to my other amp? 2. Do i just splice the amp turn on wire to the wire on my other amp? 3. Do I need a fuse for this amp? Its 250W, has a 20A fuse and im using 8g. wire. 4. All I have is 12G. wire and 18G. for speaker wire, should I get something in between them? 5. Will I get more sound if i cut holes in the rear shelf thing for the speakers? I currently dont have alot of mids in my car, im hoping these speakers will help.