Yes,, I should have said that, battery needs to match controller. I did assume you meant to run no more than 40 amps, on that battery. I wouldn't run more. 2000w, which still makes a very fun, almost motorcycle like ride. (Ok, hot moped, but still fun)
Re the regen button, I just assumed you would not grab throttle while pulling a brake lever, or pushing the button for regen. Some people need an e brake, but most folks like that can't find ES.
Normally regen is enabled by connecting your e brake wires, by grabbing the brakes. I hate the usually cheap e brake handles, so I tend to choose another way to kick on regen. I can thumb the button and grab left brake fine, or just grab brake, or just thumb the rear e brake. I like choices.
Other controllers will be fine, they just have to have a CA DP plug on it, or you have to put one on your controller. I just thought the grin 40 amps would be a good choice for the CA and PAS. Justin invented the CA, brought in the PAS capability, so it just makes sense to me to pair all that with his controllers. They do get pricy, but you are wanting the Lexus build here.
Me,, just give me a controller than functions, and a throttle, and I'm happy as a hog in shit.