Ok here is a basic setup I came up with that should get you in the ballpark..
Create your balloon, I used a nurbs sphere that I stretched and scaled a little bit. Make the balloon a rigid body. Adjust the center of mass down in Y so that it is more bottom heavy. Set impulse Y to '.5'. This will drive the balloon to rise.
Create a gravity field affecting the balloon. Set magnitude really low to '1'. Create a turbulence field, set magnitude to '10.'
Keyframing the impulse value on the balloon rigid body will drive it up/down. My balloon works pretty nice, but seems to lack that bottom heavy weight. It tumbles over itself here and there.
The string tutorial looks pretty decent, I would start there. To have particles collide is different than rigid bodies. You select the soft body particles and collision geometry and do Particles -> Make Collide instead. Then they will interact with your floor and geometry. There is an offset value in the "geoconnector" node in case the thickness of your geometry becomes a problem.