Mission 4 - After defeating 4 of the enemies Zoids on the field 6 more Zoids will appear. 4 in front and 2 in back. Just keep moving up and let the 2 at the bottom come up.
Mission 5 - Mission Six you need to take down 3 satellite within 12 turns. I found it a bit easier to send 2 sniper and a healer equip with a range cannon to the left and send the other 2 with a range cannon and a Zoid whose has the most movement per turn with a machine gun up front. Around Turn 6-8, 4 more enemy Zoid will appear at the top. This one may take some time to complete. What I did was try to take out only the enemies in the way and head straight for the satellite.
Mission 6. There are 10 enemy Zoid with range cannons. after taking out 2, 4 more will appear(2 to the bottom and 2 to the right) . After taking out 4, another 4 will appear (2 to the left and 2 to the top). Going with sniper and machine gun up close seems to be the best way for this level. Have the Defensive command skill and use that whenever you don't attack. At the start move your team to the left side of the field and hold the top and the bottom of that side.