I had a comic book that involved a charity race between Flash and Superman. The race was to be run across the galaxy and speed was limited to the speed of light, as Superman could obviously fly faster, but Flash could only run that fast. I forget how he was to breathe, I think some kind of energy shield. Flash got tired at some point, but Superman never tires. IIRC, they timed the finish to a perfect tie, splitting the finish line ribbon into three pieces. Truth is, Superman could have easily beaten Flash.
Now, as far problems punching someone into space, I think the energy required would punch right through a person’s soft tissue. He could, without question however, fling you into space, but there might be tissue issues as well.
Note I am not an expert, but am constantly amazed at what remains in one’s brain compared to what does not.
I wondet how many windows were shattered by Flash as he broke the sound barrier.