If you can, I'd wait a bit to add the CYA. Maybe you don't work tomorrow since it is Memorial Day and will have time to test it and add bleach every couple of hours? The more often you do it, the faster you'll get the conversion over with. I would also suggest taking the FC a little higher. Since the high cl reading isn't going to stick around long, it isn't going to be a concern about hurting your liner. Go ahead and take it on up to about 10. A couple hours later when you test, take it back up to 10, repeat, repeat, repeat. We have had people in the past who have gotten through their conversion quickly because of how often they added bleach.

We usually suggest getting a pool cleared up before adding CYA. As far as what brand to buy, I doubt it matters. As long as you buy cyanuric (or isocyanuric) acid, it will be fine.