1. Is this practice of connecting what seems to be three clauses by commas correct?-- Yes; it is a list.
2. Shouldn't it be the phrase "a human's" or "that of a human"?-- Yes
3. Should it be the verb "was" or "were"?-- We could argue for either, but 'was' is more natural.
4. They seem to have the best players, the worst facilities, an