1. Yes if you finish card IDing and the last flash is charm you get 2 bonus point in charm.
2. There are 5 bonus points. 1 point will go to each type(power, magic, sense, charm) the 5th point will go to 1 of the type depending on what type flashes last.
3. Yes, you can just get 3 in sense and that 1 bonus will bump it up to a 4. If seed flashes sense last then you will get +2 in sense making it a 5.
(do remember 4 bonus point if ID 800-1000cards and 5 bonus if you finish card ID meaning you ID enough cards for it to stop glowing.)
4. Hard question lol. I would suggest you get 14point before Hatching for absolute legendary. Wait for Almora or expert to tell you this.