The Cuban missions weren't part of the storyline
Anyway, I also thought Steve Scott's missions were pretty cool. He gave you a nice variety of missions
The tractor has something attached to the back that you can move up and down with the right analog stick. If you reverse into a car and move the hook either up or down(can't remember which) then the car will become attached
You get into the boxville(one near Denise's house) and push R3 between 20:00 and 4:00. You then drive to a house that has a yello indicator in front of its door and go in. You then sneak around the house and pick up items