I'm not familiar with which missions are available at which level, but when you're picking one from the pause menu, the details panel on the right will show the min and max number of players. I just opened to browse through it and shows Ballas to the Wall is open at rank 5, and can be played by one or two players.
A friend of mine showed me a trick the other night to farm an expensive Vapid Sandking truck out in the desert for selling to LS Customs. I made
a short video to show where on the map you need to go and what you need to do to trigger their appearance. Before you can start what's in the video, though, you have to do the following:
- Start the 'Denial of Service' mission.
- Blow up the first five trucks. This will kill the timer for the remainder of the mission.
- Ignore the last truck you have to destroy for now. Fly or drive out to the desert, just north of the prison (shown in my video above).
Once you get one, you can park it in a garage (I bought the closest six-car garage to their spawn location just for farming them) and go back to repeat the process. The blue ones sell for $18.5K, yellow for $17.5K. When you're done farming, you can go finish the mission and get a fat paycheck for taking so long to complete it. Also, this works with multiple people in the game.