I just beat mission 6!
Here's what you need:
Solar panel level 3
Storage level 2
2 repair stations
at least 2 THELS level 2
5-8 rockets, mostly level 3
relays
Maybe a few pulsers
All ships come from the right, so all your defenses should be there (unless it somehow changes).
Make 3 relay branches, 2 in each branch. At the end of the branches, have a rocket launcher, preferably level 3. Level 2 is must.
Build a few more rockets in between the branches. Most of the rockets should be level 3. Then build THELS to defend your rockets (AND YOUR RELAYS). The ships have a long range. THELS need to be level 2. Then, build a few pulsers to kill the small things the motherships send out.
Remember, rockets uses 5 minerals to fire.
"First off, does anyone know why I called this meeting?"
"To give me a nametag?"
"No, I'm going to kill you! Muhahahahahaha!"
*pushes button labeled Shark Tank"
Funny stuff.
Easiest way to make money late in the game:
At Hara, buy lots of fuel, at least 1000L.
Go to the closer gold miner city on the far right. Sell fuel so you have about 300 or so left. Buy gold if any (or just leave it there). Go to Qubba, sell gold. Buy crude oil. Go to Hara, sell crude oil, buy fuel, go back to Qubba. Buy jewelry if price is under 1000. (Save before this so you don't get busted.) Find a city that buys for over 4k each. Refuel, repeat.
When you have a lot of money, you can go to Qubba. Cops will fine you if they reach you (1k per). When you are confident in your sum of money, buy fuel, buy a car (the best one probably), and sell your mules+carts.
TIPS:
When you start out, make the most of your initial route. As time goes on, the price of leather and clothes start to drop.
Figure out what you can profit most from. Shoes have make a huge profit, although produced slowly.
As you make money, buy more mules and carts. Horses are a waste.
You can sell horses, carts, and vehicles for a lot of money. After a while, this becomes useless.
A DP mission requires 3mill. Good luck.
 "Don't Shit Your Pants"){kind=icon}
 "The Space Game"){kind=icon}
 "S.W.A.T. 2 - Tactical Sniper"){kind=icon}
 "Globetrotter XL"){kind=icon}
 "Mastermind: World Conquerer"){kind=icon}
 "Zombies! Apocalypse - MMO Zombies Massacre"){kind=icon}
 "Caravaneer"){kind=icon}
 "Shoe Rage"){kind=icon}
 "Farragomate"){kind=icon}
 "BubbleQuod"){kind=icon}
 "SAS: Zombie Assault"){kind=icon}
 "The Missile Game 3D HS"){kind=icon}
 "Scriball"){kind=icon}
 "Panda: Tactical Sniper 2"){kind=icon}
 "Two Rooms"){kind=icon}