It doesnt really matter to the predators what the sex is. It's is still food regardly if it's a male or female. However the age and health can be favored. Young, old, weak or sick sea lions can be targeted more simply because they are easier to kill

Yes you can. I have both pokemon gold and silver, and sometimes I trade with myself between the games to get a pokemon that only can evolve through trading.

If you trade with other trainers that are computer-controlled you cant get your pokemon back.