1. I'd recommend a floater . . . EXCEPT that fumes from it may kill the cover, at that point. 20 ppm + cover should be OK. Just take it up to 20ppm a day BEFORE you cover (top it off if necessary) and then try to stay out of the pool for 24 hours. Gases can form from that 20 ppm + people goo. Uncovered these gases escape and cause no problem; covered they could attack your cover.

2. Do NOT worry about a minimum CC reading (0.5 if using 10ml; 0.2 if using 25 mil). I'm not quite sure what that is, but I've quite sure it's not a real problem.