more questions - stereo amplifier install newbie

I am trying to install a 4 channel amp to four speakers and a sub amp.
I bought a walmart dual amp installation kit. I have my 5 gauge power wire going from the battery to a 100a fuse.

The installation kit included a power distribution box. My questions are:

How long should the power wire be from the battery before it gets to the distribution box? (does this depend on the amp?)

out of the distribution box comes two 8 gauge wires going to both power terminals on the amps.

Should I have 8 gauge grounding wire coming off the two amps, going into a grounding box? Out of the grounding box, should it be 5 gauge grounding wire going back to the battery?? If I don't need a ground box, how should I ground both the amps??

Keep the 5 ga supply from the battery as short as possible given the location of the battery. Put the big fuse on the end closest to the battery, hthe other end to one distro block. Run 8 ga from that distro block(if that gauge is sufficient for the amp(s)) positive wire to each amp. Run an 8 ga negative from each amp to another distro block, then a 5 ga to the negative battery terminal or the ground point on the block, whichever is closer. You may need more large wire, the car amp kits come with a short ground wire because they assume you are grounding to a steel auto chassis. On a boat, you need to run a longer fat ground wire to the boat ground, i.e. block or battery. If it is a long run, buy a piece of bigger wire than the short big power wire, say 4 gauge. You can get top quality 4 ga. by the foot at West Marine but you will pay top dollar, 2.99 a foot or so. Or order it online. Then, all you need is the blue turn on wire from the head unit to the remote turn on terminal on each amp. One wire from the head daisy chained to both amps will work. Then, hook up the two RCA cables. That will do it. Does that help?

Psyclone, that helps a lot thanks.
Can I buy the extra negative wire and another distro block seperately or do I have to buy another amp kit?

I think you can buy these seperately. Home depot has wire out the wazoo...I bought 18 ft. of 4 guage for my ground wire at about 99 cents per foot. It's not the pretty stuff like you get in the amp kits but it works great. So you might check there if you want to save a few bucks.

for $25 I can buy another amp kit and use the red wire and distro block that comes with that. Seems to be cheaper than buying them both seperately.

That may be the cheapest, but, use some black tape or heat shrink on the negative wire (both ends) to identify it as the ground so that you or someone else does not get confused about which one is the hot, which one is the return. You are dealing with a lot of current, a fire is a really bad thing on a boat.