Sounds good to me
Balloons are a good idea provided Mars will cooperate. Getting the compressed hydrogen to Mars would be a chore. I wonder if a clever in-situ resource trick is possible? Imagine the vehicle lands in an area rich in water ice, the vehicle extracts water from the environment, produces hydrogen from the water and then inflates little balloons with payloads in an assembly line style? The problem with these schemes is the mass of the hardware that enables the in-stu trick can be greater than the mass of the in-situ material extracted.
Gary