Howdy Riddler.. I've been watching from afar, 'Dude and the others have been guiding you welll.. It fun to watch a new owner get the hang of things!
You can start turning your SWG knob down a bit.. When mine gets to 10-ish I drop the output in 10% increments.. let it settle and see where it tests out. You will find the FC demand will increase over the summer due to the sun and bathers and then drop off in the fall. It is never static, but it is a gentle curve. It really took two seasons for me to get the feel of it so be patient.
Yup a CYA of 70 is perfect for a SWG pool.. you will see your FC retention start to go up as you approach the golden value...and you will have to tweak the % output knob to compensate.
I love doing the Alk test.. its just so fun..
Yes water additions will throw off your chem levels.. I did not see where any one suggested you run a panel of tests on the water you put into the pool. You should do that so you know how much is being added by your water additions. For example if you have really hard water, your CH will be constantly rising...
BTW a previous post you asked about taking multiple trips to the pool to get 18" deep samples... who said pool ownership wasn't going to be a workout!

I use these..
We get them from the Dollar store and are multi-purpose devices. Then I blast/fill a little 16 oz squirt bottle that is big enough to do all the tests. Don't forget to rinse!