Howdy-You're negative from the battery is should be grounded somewhere to the frame (possibly along with the engine and/or alternator) but you don't need to return the equipment ground to the battery. For example if you're fans or pumps are located with an easy run of the frame then ground directly to there. You want the least amount of resistance as possible so short runs on your 12v grounds are best. And are usually best made at two joining points on the frame (where say a strong crossmember or brace is welded to the frame). The body can be used as its aluminum but frame is best-especially since the rest of the vehicle uses the frame for it's 12v ground.
And yes that sounds perfect for the positive to the terminal block...do add some inline fuses or circuit breaker type switches though...helps keep things safe and protected. Also a larger fuse/circuit breaker on your main 12v is a good idea. Just helps protect your battery and electrical system from anything.