Yes I have idea for this, at least for floating ballon. With your guy floating there are more problems, you need to watch tutorials first (that is biggest problem). Making ragdoll out of character is not trivial, so first do just balloon. Then we see what can be done for your guy.
For floating ballon:
- create new blueprint class
- get ballon model (for eg, default sphere for testing)
- turn on on its physics
- set so it has gravity
- set mass to very small
- add physics thruster that thrusts down (red arrow should be pointing up)
- now turn thruster on, you should have floating ballon.
Or follow this: