Fully automatic cascade brewing system
This design uses a single control circuit to manage bottle flow through a series of brewing stands (1 for each step in the process, potions can take up to 5 steps to complete) It works very well for keeping a chest or dropper full of 1 type of potion, but it takes up a lot of space. Where a choice of potions is desired, a semiautomatic system like my last 1 or the fully automatic brew-on-demand systems I've seen others post would be more compact & easier to build. That said, I just added 1 of these to my blaze spawner to keep a supply of potions of harming on hand for harvesting (I tried shooting them from a dispenser, but you have to throw it yourself if you want the xp).
I went with a more vertical arrangement in my test world, thinking it would be easier to see how things were set up & worked, but the stair-step arrangement in my play world proved to be simpler to wire up.
I seem to have hit a bug where the dropper stops working in my play world. Also, sending minecarts through the nether gate is tricky. I got it to work reliably with 1 cart through my 1st gate, but am having issues using it with my water bottle filling station gate. It still beats carrying all those bottles by hand.