Ampacity of copper bus bars. Your 3/4" pipe should be fine as the load from your batteries is probably never going to be above 100-150 Amps. I used a bolt on fuse at the bus and that is probably a good idea for your project.
Midi fusesTip: Drill slow when drilling copper.
For those wishing to make there own buses with copper bar stock, I bought my bars at
Discount Steel. They have a yard close to me but they will also ship.
When I was a kid, we made our own lead soldiers. We heated lead on the kitchen stove and poured it into molds. I think I still have the molds. We also played with mercury out of thermometers, poured gas into water buckets and lit it, and I even had a Chemistry Set. It's amazing that I'm still here, lol.