1. Because there are Flak batteries on the ground firing at you, you will notice they are rectangles, not dots, which tells you they are on the ground.
2. You need to get the transports in the air so don't worry about ground targets at all.
3. Shoot them all, don't take chances.
4. Don't know, keep killing until its over.
5. You're just having a hard time, its really not that hard once you follow a few tips:
1. Get to within 200 yds before firing, throttle down and use combat flaps to avoid overshoot, approach from slightly below to avoid the top rear gunner and put *all of your fire on the engines*. Thats the most important thing to finishing the transports off quickly, if you aim for the fuselage, it will take you forever whereas one good burst to the engines can bring down a JU-57 in an instant.
2. Use your map ALOT. Once you bring down one group, look on your map to see where the next is and open up your throttle and raise flaps to zoom over there.
3. Ignore everything else, just kill the transports as efficiently as you can and you should be fine.
check out this IL-2 vid for some anti-bomber tips: