Would "jesién jest porą roku" also be accepted?
Are "pora roku" and "okres" completely the same thing?
no. "Pora roku" = "season of the year", "okres" = "period".
'the fall' not 'fall' I think. Fall is not the name of the season.
Autumn is the official name of that season in English. However, Fall is used as well. "The leaves fall in Fall." Spring, Summer, Fall and Winter would be acceptable names of the seasons.
Fall is American English, autumn is British English.