Im not saying your wrong im going off what I have experienced first hand, You ask just about anyone with some common sense in the car audio field where to ground and 99% of the time the response will be "if possible straight to frame cleaned to bare metal" That my friend is how i have done it sense my jeep about burned to the ground from a bad ground,
Big 3 is done, I had (up until about 1 hour ago) a voltage meter hooked up to my amp to measure the voltage. Its funny because even though you would have ALL that done i only had a stock alt, Group 34 batt and the big 3 done and really didn't have any voltage drop once i fixed my ground. No im not trying to be a know it all, Im sharing with YOU knowledge that i know, stuff that i have known sense i started putting systems in. Correct me if i am wrong, until then i will keep on keepin on.
Also i did answer your questions minus one because i didnt see that one, the specs on the amp @1 ohm is 1500, Clamped it might do 1k