For Bus Bars this is where I started:
Engineering high quality marine electrical components for safety, reliability and performance
www.bluesea.com
I decided on the 1000 amp, 8 post 3/8", which ended up being about a foot long. I got two of these, one for the positive and one for the negative.
Lessons learned from that: I needed 7 posts, but not 3/8", so they are available in a variety of sizes and posts. I only needed two 3/8" Posts, the other four could have been #10, and that would have made the busbar much smaller. The ones I got are a little short of 12" and both together take up my 2' wide power board from left to right. I also wish I'd purchase something with a cover.
I originally went with 250 amp audio busbars, four post, but my build outgrew that. I also don't feel good about using an audio busbar for PV. In general audio electronic components do not meet standards I'd like to see such as less expensive ANL audio fuses are not rated to be the main battery fuse like the more expensive Blue Sea ANL fuses that have the same amperage stamped on them.
So, Blue Sea makes quality products that are rated for build like we are doing.
Edit: From my Battery negative terminal, I have a two or three foot run of 4/0 wire attached to my battery shunt, and then there is six inch 4/0 cable to the Battery Negative busbar.