1) Generally when you take out all the enemies, you all get into the truck and leave before the BMP arrives. But on those occasions that it takes you longer to leave, try to be the last one in. If you see the BMP coming in, call him out to your commander. He will order everyone out of the truck and have the RPG man take out the BMP.
Generally it takes the BMP quite some time to arrive and it makes alot of noise far before it gets to you.
3) It is blackbears job to take out the tank, not yours. And they generally succeed. You can help though. The only way to help is to remain hidden and unseen until the tank is dead. If you are spotted prematurely, the enemy will be alarmed and the tank will start moving before blackbear is ready.
So sit tight and report in enemies(this is done by a certain key in your settings) until that tank is destroyed.
4) There is a certain button in your settins options that allows you to report in enemies to your commander. Check your keys options. You must press this button while your crosshairs are directly ON an enemy target.
5) No, you just need to be vigilant. Enemies don't spawn or appear. It's just that someone else spotted it before you.
Lastly, this is an easy mission. It just takes patience and strong nerves(also alot of accurate shooting) Don't get so rattled by the sound of the nearby BMP. It takes a while for it to appear.