Thank you for your reply, I think I have some answers for those questions.
1) it's probably PRS and coyote hunting mainly in prairies( have deer scope 3-9)
If you seriously consider PRS as a sport, then you may want to get one scope from the following list. A clear, crisp glass becomes very important when you pass 500 meters. Try to look through S&B, Steiner, Kahles, NF, Razor II and you will never want to look again through a scope that costs $500. For PRS you definitely need a FFP scope preferably with H58/H59/Tremor reticles. They are expensive.
2) 3) I can go both no problem imperial and metric. Just don't have an experience with scope calculations, what is better?
How can you go both if you don't have an experience with scope calculations? Try to calculate in your head the target and distance with MOA and then with MILS and see what do you prefer? I used to be a MOA guy, but recently switched to MILS and found it to be much easier to calculate.