q1: check out this gui calc, may help you
https://thesilphroad.com/researchq2: the % is how much of the combined atk def and stam your pokemon has out of the total 45 points (15 for each stat is 100%)
The CP is is based on the IV stats and the poke's level. That arc line that fills up as you use star dust is what level the pokemon is compared to the player level. The pokemon can be 1.5(?) levels higher than the player level
So you can have a high level CP with bad IV = roughly equals a higher level pokemon
and a low level CP with perfect IV = a low level poke
Move set and IV stats are what is important.
In the short run CP only matters if your trying to determine if you want to invest star dust to get CP higher.
If it has bad stats with (relatively) high CP, dont use stardust
If it has good-great stats with random CP, maybe
If it has Perfect stats with random CP, probably worth while unless you want to hold out for a naturally higher level Pokemon