Here is a picture that might help you in hooking up your amps and speakers. Hope it helps.
As for your other question; if your distribution block can handle two 4 Ga cables then go for it. But, I would consider upgrading to a 2 Ga or even 1/0 Ga supply wire running to your distribution block and battery sometimes in the future.
The fuse at your battery is basically protecting your cable running from the battery to the distro block and not neccessarily your amps or equipment. If your supply cable shorts out to ground, it would get extremly hot and could catch fire or ignite your carpet/upholstery/seats/girlfriend etc...
A 60 amp fuse should be the right size for your 4 Ga supply wire. Use 100 amp fuse for 2 Ga. 120 amp fuse for 1 Ga and 150 amp for 1/0 wire. The danger with using a 100 amp fuse with a 4 Ga cable is that the fuse might not blow and let the cable overheat and do bad stuff to your car.
If you decide to get a distro block with fuses for each circuit, then use a 20 amp fuse for your 8 Ga cables.