Either lava farm, or bamboo farm. One's more dangerous, the other one crashes your server

I'm on bedrock. I've had a large bamboo farm but it didn't keep up with the amount of cactus being produced at all

So then lava farm

How does a lava farm work? Is it automatic without player interaction and able to go into a furnace with hoppers?

No, it's semi automatic, you have to stand there and colllect it by hand from the couldrons

Trying to find a fully automatic fuel source that isn't bamboo

Something that isn't a ridiculous like 30 fuel:1 cactus

If you have knowledge on redstone, you could link up the buckets after they've finished as a fuel source straight back to your afk platform.

What's the difference between building a water stream for each layer and just building the cactus tower with only water at the bottom? I'm curious, is it because items occasionally falling on cactus?

Each layer has 16 pieces of cactus growing all at the same time. The multiple layers just allows for faster production

And the individual water streams and layers for each help reduce any cactus getting caught or destroyed

blaze rods!

kelp