Yep, you're really getting it all. And yes, we're assuming algae is gone because of the passed OCLT.
The FC daily extinction will be whatever is needed to eliminate contamination plus whatever is lost to the UV radiation from sunlight. CYA makes FC last longer by protecting most of the FC by holding it in a buffer system, which reduces the speed that FC is lost to sunlight. As the harsh part (the active part) of chlorine gets used up, the CYA "releases" more chlorine to become active chlorine which can eliminate contamination. At any given time, there is very little "harsh" or active chlorine in the water, because the CYA essentially "holds" FC in reserve, to be available as needed. The more CYA there is, the more the FC is protected, yes.
Your SWG makes fresh chlorine which becomes part of the buffer system, and replaces the chlorine that gets used up, whether it is lost to sun, or used for decontamination. So now you'll dial in your SWG to cover the daily losses of FC. The daily losses might average 2-3 ppm FC per day, so the SWG has to make approximately that amount. On a super hot heavy swim day with lots of fun in the pool, the loss will be higher, maybe even 4 ppm FC. A cloudy cool day, with no one swimming and super clean water, the loss might be only 1 ppm FC. You'll see this in your testing if you test daily for a while.
Say we set the SWG to make 2.5 ppm FC per day. If you have an easy day, and only 1.5 PPM FC is used, your pool FC will rise by 1.0 ppm FC. If you have a pool party, and it's hot and sunny, and it takes 3.0 ppm FC that day, your pool FC will drop by 0.5 ppm FC.
Boost simply turns the SWG to 100% and possibly a 24 hour period, or steady until midnight, or something like that. I don't know your SWG or controller well enough to say. But I can say it is not shocking. It might add a few extra ppm FC, nothing like shocking. I use my boost for about 12 hours for a party, and it adds about 2 ppm FC extra, to absorb the extra bather load. And yes, you've got it. It is dumb and just pumps out some extra chlorine.