Hi, and welcome to the forum!
As professional engineer who has built a number of drivers, I can say that switches, modes and groups are easy, it's just how much software do you want to write.
As for boosting nearly 30W out of an 18650, that'll be a lot more of a challenge. With plenty of space, I could do it. But to fit in 23.5mm circle? I'd have to work on it a while to even decide if I could do it. I suspect the answer would turn out to be no.
On the optimistic side, Linear Technologies (recently purchased by Analog Devices) makes some pretty impressive modules with all of the hard part integrated. They are generally step down, not step up, but they might have one that could be coaxed into doing what you want. Unfortunately, they are neither cheap nor easy to assemble.
Any way you look at it, this is not a task for a noob.
By the way, do you realize this light would only run about 20 minutes per charge at full power?