Which pokeball you using?
If you use a regular one, a dizzy Pokemon under Wild Zone 18 will have 3-5 stars, alphas not counted.
Alphas have 0 catch rate with a regular pokeball unless you have INSANITY level luck.
Quick Balls, Ultra Balls, and Timer Balls are recommended for catching.
I am afraid all other info are to be confirmed, because I have not played the game yet.