Some Of Yall Construction Gurus......

I'm going to suggest very seriously talking to the company who engineered that building. The outer skin is part of the structure on them just like a pole barn. If you take it off to open it up, you will alter the parameters for which is was designed and it could compromise the structural design. Might never be a problem, or the first high wind situation might blow it down.
Not an issue at all. I sold these buildings for a year and they use the exact same frames for the open sided carports as they do for the fully enclosed garages. As long as he has his new beam supported properly and fastens the existing rafters to the beam, he’ll never have a problem.